Unit 8: Introduction to Genetics

Test on: 2/3/12

IntroAlthough the resemblance between generations of organisms had been noted for thousands of years, it wasn’t until the 1800s that scientific studies were carried out to develop an explanation for this. Today we know that we resemble our parents because of _______, which is the set of characteristics we receive from __________. The study of heredity is known as ________.

heredityour parents

genetics

I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275-278)

In sexual reproduction, an egg and sperm cell fuse together to create a fertilized egg or ________. Egg and sperm cells are known as _________. Gametes are the only cells in the body that are not produced by ________.

zygotegametes

mitosis

I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275-278)

Instead gametes are created through a special process of cell division called __________ which _______ the chromosome number. Meiosis only occurs in the _________ of females and the ________ of males.

meiosis halves

ovariestestes

A. Chromosome Number

1. Human _______ cells, or body cells, contain ___ chromosomes. Somatic cells are ________ or ___ because these cells contain a ______ set of chromosomes – half (___) from ______ and half (___) from ____. These “matching” chromosomes are known as _______________. A homologous pair is a pair of chromosomes – one from each parent, with the same ___________ or _______.

somatic

46diploid 2n

double

23 mom 23dad

homologous pairs

type of traits

genes

A. Chromosome Number

2. Human gametes (____ and ______) contain ____ chromosomes. They are ______ or __. These cells contain ___ the total number of chromosomes, a _______ set of chromosomes. When the gametes fuse together in ___________, the resulting ________ has _______ chromosomes.

egg sperm23

haploid n 1/2single

fertilizationzygote 46

B. Formation of Gametes: Meiosis

Gametes are formed in meiosis – a special type of cell division that only occurs in the _______ of females and ______ of males. In meiosis, DNA is replicated once in ___________________, but the cell goes through two cell divisions, resulting in ___ cells with _______ the original chromosome number.

ovaries testes

S phase of the cell cycle 4

1/2

Meiosis occurs in two stages: 1. Meiosis I

Prior to meiosis I, the DNA is replicated in ____________________________. When the chromosomes, each consisting of 2 _______________ line up in the middle of the cell in __________ I, they line up in ___________ pairs. In anaphase I and telophase I, the homologous pairs __________, but the sister chromatids and _____________ are still intact.

S phase of the cell cycle (or interphase)

sister chromatids metaphase

homologous

separatecentromeres

Meiosis occurs in two stages: 1. Meiosis I

Two cells are formed, each with ___ pairs of _______________ making up ___ chromosomes, but there are no longer any ________________ present, so the two cells are ____________.

23 sister chromatids23

homologous pairshaploid or n

Meiosis occurs in two stages: 2. Meiosis II

The process continues with the two cells formed moving directly into prophase II without any further ________________. After the chromosomes align in the middle of the cell in __________ II, this time the sister chromatids are pulled apart in _________ II.

replication of DNA

metaphase

anaphase

Meiosis occurs in two stages: 2. Meiosis II

Two new cells are formed from each of the two cells formed in Meiosis I, resulting in a total of ___ new cells, each with ___the original number of chromosomes. The cells produced are called _______.

4 1/2

gametes Therefore, meiosis results in 4 haploid gametes

C. Crossing Over

Crossing over occurs during ___________ when ___________ pairs of chromosomes come together. A portion of one ______________ may be broken off and exchanged with the corresponding portion of a sister chromatid of the homologous chromosome. Crossing over is very

common and __________ the genetic variability in offspring.

prophase I homologous

sister chromatid

increases

II. HISTORY OF GENETICS (pp. 263-270)

A. Gregor Mendel Known as the “Father of ________”, Mendel

is famous for his experiments with ____ plants. He used true-breeding pea plants, which means _______________ and characteristics always show. This generation of true-breeding plants is known as __ generation. Mendel studied seven ____, including plant height, seed color, flower color, etc.

Geneticspea

purebred, pureline

Ptraits

II. HISTORY OF GENETICS (pp. 263-270) A. Gregor Mendel

A trait is an _______________. Pea plants cross-pollinate, meaning pollen from one plant fertilizes an egg from another, but they can also self-pollinate, meaning pollen can fertilize egg from _____ plant. Mendel controlled the fertilization process of the pea plants by preventing ______________ and controlling ______________.

inherited characteristic

same

self-pollination

cross-pollination

II. HISTORY OF GENETICS (pp. 263-270) B. Mendels’ Results

• 1. P generation – Crossed _________ plants with one trait with ________ plants with the other. For example, _____________________

purelinepureline

tall plants (TT) X short plants (tt)

II. HISTORY OF GENETICS (pp. 263-270) B. Mendels’ Results

2. F1 generation – Offspring produced from _____. In F1, one trait seemed to ________. For example, tall plants X short plants = ___________.

3. F2 generation – Offspring produced

from _______. In F2, trait that disappeared in F1 reappeared in ____ of the offspring; the other ¾ showed ______________.

P x Pdisappear

all tall plants

F1 x F1

1/4

trait seen in F1 (dominant trait)

II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles

After analyzing his results carefully, Mendel

formed conclusions that increased

understanding of inheritance and opened

the door for the study of genetics.

1. Individual units called _______ determine inheritable characteristics. A gene is a portion of _____ that codes for a specific ______.

genes

DNAtrait

II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles

2. For each gene, an organism inherits two alleles, one from each _______. Alleles are different forms or _____________ of a ______.

a. If the two alleles are the

same, the organism is said to be ____________ for that trait and the allele will be expressed.

parent

versions gene

homozygous

II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles

b. If the two alleles differ, the organism is said to be __________ for that trait and only one allele will be expressed. The expressed allele is the ________ allele, designated by an _____-case letter. The allele that is not expressed in a heterozygous trait is ________, designated by a _____-case letter. A recessive allele is only expressed when an organism is ___________________.

heterozygous

dominantupper

recessivelower

homozygous for that allele

II. HISTORY OF GENETICS (pp. 263-270) C. Mendel’s Principles

3. In meiosis, the two alleles for a trait segregate (_______). Each egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. Due to the random separation of chromosomes in meiosis, there is a ____ chance that a copy of that allele will end up in the gamete produced. This is known as the principle of segregation.

separate

50%

II. HISTORY OF GENETICS (pp. 263-270) D. Genetics Terminology

1. Phenotype - ________ description of trait; for example, ______________

2. Genotype – Genetic make-up of an organism or set of alleles; for example, ____________

3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, round is designated __ and wrinkled is designated __.

Physicaltall, short

TT, Tt, tt

Rr

II. HISTORY OF GENETICS (pp. 263-270) D. Genetics Terminology

a. Homozygous dominant for pea seed shape is written ____. Seed shape? ______

Genotype = ___; Phenotype = ______

b. Heterozygous for pea seed shape is written ____. Seed shape? _______Genotype = ___; Phenotype = ______

c. Homozygous recessive for pea seed shape is written __. Seed shape? _________Genotype = ___; Phenotype = _________

RR roundRR round

Rr roundRr round

rr wrinkledrr wrinkled

III. ANALYZING INHERITANCE (pp.135-137)

A. Probability Due to the law of segregation, if you know

the genotype of the parents, you can predict the likelihood of a trait occurring in the offspring. Probability can be written 3 ways. The probability of a coin coming up heads after being flipped is (fraction) _____, (ratio) ________, or (percent) _______.

1/2 1:250%

III. ANALYZING INHERITANCE (pp.135-137)

B. Punnett Squares

A Punnett square is a tool used to predict the possible outcomes of ________ and

___________; in other words, a Punnett square is used to determine the probability of certain traits appearing in offspring.

meiosisfertilization