Ch. 5 Meiosis and Genetics.notebook - Crestwood …. 5 Meiosis...Ch. 5 Meiosis and Genetics.notebook 1 ... Meiosis 5‐3 ** We are starting with section 3 because in ... Nov 101:44

Ch. 5 Meiosis and Genetics.notebook

1

January 04, 2012

Nov 1011:15 AM

Meiosis5‐3

** We are

starting

with sec

tion 3 be

cause in

order to u

nderstan

d Genetic

s, we mu

st first

understan

d how th

e cells a

nd chrom

osomes

divide to

form the

gametes

!

There are many types of reproduction...

~ binary fission - done by bacteria

~ asexual - just split in half - amoebas

~ fragmentation - pieces split off and each piece becomes a new organism - starfish

~ budding - whole organism grows off another and then splits off - hydra

~ parthenogenesis - female makes a viable egg that grows without being fertilized - water fleas

~ sexual - 2 parents give genetic material to make offspring that are genetically different from them - most eukaryotes

* advantage - genetic diversity!

Just know the ones that are highlighted!


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January 04, 2012

Nov 1011:27 AM

* Remember that homologous chromosomes are chrom. of the same type

ex: chrom. 1 from mom is homologous to chrom. 1 from dad

Germ cells give rise to gametes - sex cells...sperm and eggs!* when gametes from the parents combine, the result

is called a zygote

gametes = haploid = 1 of each type of chromosome (1n)

zygote = diploid = 2 of each type of chromosome (2n)

so for humans, in each gamete the 1n = 23 in each diploid cell the 2n = 46


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January 04, 2012

Nov 1011:35 AM

We have already looked at making more body cells through mitosis...

Let's look at how to make the gametes through Meiosis!

** Meiosis is cell division that makes daughter cells with half the number of chromosomes than the parent cell.

2 divisions take place:

Meiosis I - first division Meiosis II - 2nd division


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January 04, 2012

Nov 1011:43 AM

Meiosis I - first division

~ Prophase I - chrom. condense- nuclear envelope breaks down- homologous chrom. pair up- crossing over can occur


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~ Metaphase I- spindle fibers move homologous chrom. to middle of cell- homologues remain together


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Nov 1011:47 AM

~ Anaphase I- homologous chrom. move to opposite poles

Note! Chromosomes DO NOT separate at the centromere at this stage!!


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January 04, 2012

Nov 1011:49 AM

~ Telophase I- chrom. gather at poles- cytoplasm starts to divide

~Cytokinesis - cytoplasm divides


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January 04, 2012

Nov 1012:06 PM

Now we have 2 cells with 1/2 the # of chromosomes...

BUT we still have 2 chromatids on each chromosome!! We now need to split these up!

Meiosis II

~ Prophase II- new spindles form


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January 04, 2012

Nov 1012:12 PM

~ Metaphase II- chrom. line up in middle


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~ Anaphase II- chrom. divide at centromeres and chrom. move

to either pole


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January 04, 2012

Nov 1012:20 PM

~ Telophase II- nuclear envelope forms around each set of chrom.- spindles disappear- cell begins to divide

~ Cytokinesis - cell divides

This results in a total of 4 new haploid cells that are genetically different from the parent cell!

When this process occurs, the homologous chromosomes will be randomly distributed

~ called independent assortment (we'll talk more about this later!)

Also, the fertilization of gametes is random as well! ~ there are about 64 trillion combinations of chromosomes!!

FYI:


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January 04, 2012

Nov 101:44 PM

Mendel and His Peas! 51

Genetics study of heredity* Research done by Gregor Mendel

(1822 1884)

began research by studying pea plants and noting traits that were passed down through generations

he went further by counting the # of plants with certain traits in each generation

led to today's way of research


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January 04, 2012

Nov 102:42 PM

Why peas?

1.) Many varieties exist easy to tell the difference between them

2.) One of the 2 forms of each character would disappear in a generation and then reappear in the next easy to count this

3.) Fast growing and produces many offspring

4.) Easy to crosspollinate

*Note* peas are self-pollinaters they don't need another flower to reproduce

Mendel removed the male parts of one flower (stamen) and removed the female parts from another (pistil). He used the opposite to fertilize the other flower. Cross-pollination


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January 04, 2012

Nov 102:52 PM

Mendel's experimental design:

3 steps…

1.) Allowed each pea plant to self pollinate for several generations

this ensured true-breeding offspring only displays one form of a trait

ex: all flowers are white and only make other white flowers when bred

* P generation = parent generation


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January 04, 2012

Nov 102:56 PM

2.) Crosspollinated 2 P gen. that had contrasting traitsEx: purple flowers with white flowers

* F1 generation = first filial gen.

Noticed all flowers of the F1 gen. were purple!


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January 04, 2012

Nov 103:02 PM

Dominant traits trait that remains seen (expressed) in F1 gen.

Recessive traits trait that is not seen (not expressed) in F1 gen.

3.) Allowed F1 gen. to self pollinate one time

*F2 generation = second filial gen.

*These are the plants that he counted!

Observed a 3:1 ratio in F2 gen. every time!

*Noticed that the recessive plants were true breeding when allowed to selfpollinate.

*Also noticed that the dominant plants were producing 3:1 ratio when they selfpollinated!

**This meant the 3:1 ratio in F2 was really 1:2:1!

1 plant = dominant , truebreeding

2 plants = not truebreeding

1 plant = recessive , truebreeding


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January 04, 2012

Nov 1511:46 AM

Traits and Inheritance52

For each trait, you get one gene from Mom, one from Dad*each gene may not have the same info!

Same info = homozygous

EX: has two purple genes or two white genes

Different info = heterozygous

EX: has one purple gene and one white gene

*Each copy of a gene is called an allele


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January 04, 2012

Nov 1511:51 AM

Genotype the set of alleles that an individual has

EX: if we have a true breeding purple flowering plant, then it must have two dominant alleles = homozygous dominant is then its genotype!

Phenotype how a trait looks when expressed

determined by alleles that code for that trait


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January 04, 2012

Nov 1512:24 PM

Probability and Punnett squares!

When we look at the alleles, we use symbols to represent the traits…

*CAPITAL LETTERS = DOMINANT*lower case letters = recessive

**Must use the same letter to represent the two forms of one gene!

Ex: For height, you might use T for the dominant tall and t for recessive short.

~ Each trait has 2 alleles so you must write the letter for each allele!

Ex: homozygous dominant = TT homozygous recessive = tt

heterozygous = Tt

*ALWAYS write dominant first for each trait!


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January 04, 2012

Nov 229:34 AM

Probability:the likelihood that a certain event will occur

Can determine probability like this…

Probability = # one kind of possible outcome total # of all possible outcomes

Q: If there are 20 pea plants being tested for height, and 15 of them had the dominant tall height; 5 had the recessive short height… what is the probability of being a short pea plant?

A:P = 5/20 1/4 So, there is a 1 in 4 chance the plant will be

short!


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January 04, 2012

Nov 229:41 AM

Monohybrid crosses: cross that provides data about one pair of contrasting traits

EX: *both parents are homozygous for their trait

you could write... one is TT one is tt

* can also both be heterozygous

for their trait

you could write...*both are Tt

* or can be mixed

you could write... one is TT one is Tt


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January 04, 2012

Nov 229:48 AM

Can use a Punnett square to predict the probable outcome of a cross!The ratios are very different from each other depending on what you are crossing…

Ex: TT x tt

We can also figure out the ratios (or probablities) by counting the phenotypes and genotypes!

Phenotypic ratio:

Genotypic ratio:


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Nov 2212:16 PM

Let's cross these! Tt x Tt

Phenotypic ratio:

Genotypic ratio:


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January 04, 2012

Nov 2212:15 PM

Let's try this combo! TT x Tt

Phenotypic ratio:

Genotypic ratio:

If you want to get a bit more difficult, I can show you a dihybrid cross! Just for fun and extension...watch this!


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January 04, 2012

Nov 2212:25 PM

Incomplete dominance: both traits are shown as a mix or blend of the two traits

* neither allele is dominant

Ex: a white flower x a red flower = pink flowers in F1 gen.

More about Traits!


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January 04, 2012

Nov 309:36 AM

Codominance: two dominant alleles are expressed at the same time

Ex: homozygous red horse x homozygous white horse= a roan horse

both red and white hairs are found on the horse's coat

Red Roan Blue Roan


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January 04, 2012

Nov 309:41 AM

Multiple Alleles: traits that have genes with more than 2 alleles

Ex: blood types A B oA and B are dominant o is recessiveA and B are codominant to form the AB blood type

So… can have 4 different blood types with many combinationsAA, Ao BB, Bo AB oo

**Note with mult. alleles, you may see them written like this:

IAi or IAIB

Let's do a punnett square to see how blood types are passed down:


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January 04, 2012

Nov 3010:41 AM

Polygenic traits:*traits controlled by more than one gene are polygenicex: skin color in humans dozens of genes

ex: eye color at least 3 genes code for color~ generally, brown is dominant to green which is

dominant to blue

**This is a basic explanation but there are actually more genes that give us the vast array of eye color!

*All polygenic traits are complex!** if you would like to research more, please do so for extra credit!


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January 04, 2012

Nov 3011:16 AM

Environmental factors:*some genes are triggered to work in

different conditions

Ex: arctic foxes and hares: white fur in winter, brown fur in summer

~the temperature triggers genes to be turned on or off which changes the fur color!


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January 04, 2012

Nov 3012:00 PM

Pedigrees!Tracking traits in families: can determine your pedigree (family history) by noting the traits your family members show or have!

Here's how a pedigree works:

circles are femalesquares are maleshaded in means they express the traitnot shaded means they do not express the traithalf shaded means they are a carrier of the trait

~horizontal lines connecting male and female indicates marriage

~vertical lines or brackets indicate their children

~ Let's look at a basic dom/rec. trait...tune deafness!

Lets look at a sexlinked trait...

Documents

Ch. 5 Meiosis and Genetics.notebook - Crestwood …. 5 Meiosis...Ch. 5 Meiosis and Genetics.notebook 1 ... Meiosis 5‐3 ** We are starting with section 3 because in ... Nov 101:44