Living Environment Name ________________________________________ Genetics Guided Notes

Mendelian Genetics

Where did we come from? Where are we going? Why are we learning this?

During the cell cycle, we talked about interphase being the time the cell carries out normal life functions, the cell

grows and the cell replicates or copies its DNA. Interphase happens for both mitosis and meiosis. So, we need

to learn how replication takes place, or how we get copies of DNA in each of our cells. Eventually, we will even

learn how that DNA makes us who we are by expressing genes.

We also talked about how during reproduction, genetic information (DNA) is passed on to offspring. So, we

need to see how that is possible at the chromosomal level. We will look at heredity or the inheritance of traits

from our parents. In asexual reproduction, offspring are clones of the parents; whereas in sexual reproduction,

the offspring are different from their parents. What accounts for that variation in sexual reproduction and not

in asexual? Why is learning all of this important? Let’s take a closer look…

I. Brain Pop - Heredity a. We inherit our looks, height, size and chemical make up from our parents

b. Heredity is passing of traits from parents to offspring

c. Every living thing inherits traits

d. Gregor Mendel studied how height, color and shape are inherited in pea plants

e. When Mendel crossed tall plants with short plants he noticed only tall plants were produced. Whatever

produced the short plants seemed to disappear.

f. Mendel called the height trait a dominant factor because it dominated or covered up the short height form. He called the short height trait the recessive factor.

g. A Punnett Square lets you predict what you would get if you crossed a tall plant with a short plant.

h. An offspring gets one allele from each parent.

i. Mendel studied over 30,000 pea plants over an 8 year period.

j. What did you learn from this brain pop?

II. Brain Pop – Genetics a. Genes are made up of DNA

b. DNA is arranged in pairs of strands called chromosomes. In humans, there are 23 pairs of chromosomes in

each cell.

c. You get your genes from your parents – 23 chromosomes from your mother and 23 chromosomes from your father. The genes from your parents combine to form your genes.

d. Sex cells are special because they have only a half set of genes.

e. Genes don’t determine everything. Factors like environment and nature can play a role too.

f. What did you learn from this brain pop?

III. Traits a. Discovered by Gregor Mendel in the mid 1800s when he was working in a

monastery. He worked with pea plants, and observed predictable patterns of inheritance in the offspring.

b. His work was considered reilable because he tested thousands of plants over many years.

c. Known as the “father of modern genetics”

d. Gene = a segment of DNA (on a chromosome) that contains the code for a specific trait Genes are determined by your parents

e. Trait =a characteristic that is passed from parent to offspring

through genes Examples: hair color, eye color, skin color, height Traits are determined by your genes which are made of DNA

trait

phenotype

f. Allele = different variations of a trait, can be dominant or recessive Examples: brown hair, blonde hair, red hair Alleles are variations of traits, so they are made up of DNA

g. Dominant = the trait that gets expressed in homozygous or heterozygous state Dominant does not mean it is the most common. Having more than 10 fingers or toes (polydactyly) is actually dominant, but just not common. The same is true for certain types of dwarfism.

h. Recessive = the trait that is masked in the heterozygous state, but show in the homozygous state

i. Genotype = the genes for a trait (ex: Tt, TT, tt) *What are some of your genotypes from lab?

j. Phenotype = the physical make-up (ex: blue eyes, brown hair); how you appear *What are some of your phenotypes from lab?

k. Homozygous = 2 of the same allele for the same trait, can both be dominant or recessive Also can be called pure or true breeding because you always get the same results. *Were you homozygous for any traits from the lab? Which ones?

l. Heterozygous “hybrid” = 2 different alleles for the same trait *Were you heterozygous for any traits from the lab? Which ones?

m. Multiple alleles = genes that exist in a large number of allelic forms Ex: Blood types - IA, IB, Ii

n. Codominance = occurs when the contributions of both alleles are visible in the phenotype

Ex: pink flowers (mix of red and white), calico cats, brindle dogs

o. Pedigrees = diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next

p. Punnett Squares are used to determine the outcome of a particular cross or breeding experiment and is

used to determine the probability of an offspring having a particular genotype

Write in

each of the

father’s

alleles here Write in

each of

the

mother’s

alleles

here

1. Write in the father’s alleles on the outside of the box across the top

2. Write in the mother’s alleles on the outside of the box along the side

3. Write in the combination of one of the father’s alleles and one of the mother’s

alleles in each box.

GENES

Dominant Recessive

DNA traits

chromosomes alleles

mother father

Homozygous –

2 of the same allele Heterozygous -

2 different alleles

Made up of

Found on

Determine your

Which have 2

One from One from

Can be

Can only be Can be

Can be