Biology Ch. 10

1
BiologyCh. 10

• Sexual Reproduction and Genetics

2
I. Meiosis

• A. Homologous Chromosomes
• - pairs of chromosomes that are very similar

- one member of a pair comes from each parent
3
B. Diploid

• - a full set of homologous chromosomes (2n)
• - in humans 46 (23 pairs)
• - in pea plants 14 (7 pairs)

4
Human Chromosomes(23 homologous pairs)
5
C. Haploid

• - a half set of chromosomes (1n)
• - occur in Gametes (special reproductive cells
  sperm and egg)

6
D. Process of Meiosis

• - specialized cell division in which the
  chromosome number is cut in half
• - homologous pairs of chromosomes are separated
• - produces gametes
• - occurs in 2 stages

7
1. Meiosis I

• a) similar to mitosis, but, during metaphase,
  homologous chromosomes come together to form a
  tetrad
• b) Crossing-over occurs exchange of genes
  between homologous chromosomes
• c) 2 cells are produced that contain 1 replicated
  chromosome from each homologous pair

8
Meiosis I
Homologous chromosomes exchange DNA align on
equator
Homologous chromosomes pair and cross over
Homologous chromosomes move to opposite poles
Metaphase I
Telophase I
Anaphase I
Prophase I
9
Crossing Over
Purple
Long
SisterChromatids
Purple
Long
red
round
SisterChromatids
red
round
old combination
new combination
new combination
old combination
10
Chiasmata
Crossing-over in a tetrad of a grasshopper. Each
cross-over is called a chiasma. This example
shows 5 chiasmata.
11
2. Meiosis II

• a) similar to mitosis but DNA replication does
  not occur before division
• b) 4 haploid daughter cells are produced

12
Meiosis II
Link to John Kirks excellent animation of Meiosis
FourHaploidCells
Prophase II
Anaphase II
Metaphase II
Telophase II
13
Spermatogenesis
Oogenesis
14
D. Importance of Meiosis

• - provides genetic variation in the next
  generation
• 1. Independent Assortment
• - chromosomes randomly assort during meiosis
• - results in gametes with different
  combinations of chromosomes
• - for pea plants, 27 128 different
  combinations

15
The Independent Assortment of Homologous
Chromosomes in Meiosis
16
2. Crossing over

• - produces recombined chromosomes that carry
  genes derived from two different parents

17
The Results of Crossing over During Meiosis
18
3. Random Fertilization

• - combines chromosomes from 2 parents
• - results in in over 70 trillion possible
  combinations of genes from any 2 parents

19
II. Mendels Laws of Heredity

• Heredity
• - the passing of traits from parent to offspring
• Genetics
• - the study of heredity

20
Early Idea about Genetics
Homunculus
21
A. Gregor Mendel

• - father of genetics
• - Austrian monk
• - developed the basic principles of Heredity
  (1880's)

22
B. Mendels Experiments

• 1. Used garden peas
• - several crops per year
• - small, fast growing
• - developed "purebreds"

23
- easy to control pollinate
Pistil(female)produceseggs
Stamens(male)producepollen
Pea Flower
24
- seven distinct, inherited traits
25
2. Used math and statistics to support theories

• 3. Published results in 1859
• - rejected by academic peers
• - in 1900 his work was rediscovered

26
P
F1
27
F1
F2
28
III. Principles of Heredity

• A. Concept of Unit Characters
• - traits are controlled by "factors" (genes)
  which occur in pairs
• - one from each parent

29
B. Principle of Dominance and Recessiveness

• - some alleles dominate, or mask, the affect of
  other alleles
• - Allele one of the "versions" of a gene

30
C. Law of Segregation

• - during meiosis (production of gametes), each
  pair of genes separate

31
Cross Fertilization of Parents
Pollen
Cross-Fertilize
pp
PP
Pollen
Pp
All Purple-flowered (Heterozygous) Offspring
32
Self-fertilization of F2
Pp
F1
Self-Fertilize
75 Purple25 White
PP
Pp
Pp
pp
F2
F2
F2
F2
33
1. Gametes

• - specialized, reproductive cells (sperm,
  egg)
• - have 1/2 a set of chromosomes

34
1. Gametes
- specialized, reproductive cells (sperm,
egg) - have 1/2 a set of chromosomes

• 2. Genotype
• - genetic make-up of an organism
• 3. Phenotype
• - physical appearance of an organism

35
4. Homozygous

• - alleles in a gene pair that are identical
• - TT or tt

5. Heterozygous - alleles in a gene pair
that are different - Tt
TT
Tt
tt
36
D. Principle of Independent Assortment

• - alleles separate randomly during meiosis

37
IV. Applying Mendel Principles

• A. Probability
• - the likelihood that an event may happen

38
B. Rules of Probability

• 1. Product Rule of Probability
• - when events occur in combination, the
  probability of each event is multiplied by the
  probability of the other

What are the odds of rolling 3 tails in a row?
1/2 x 1/2 x 1/2 1/8
39
2. Probability has No Memory

• - Previous events do not influence the
  probability of future events

The odds of rolling 3 tails in a row are 1/8.
What are the odds on the next toss being a tail?
1/2
40
V. Gene Linkage and Polyploidy

• A. Gene Linkage
• - Chromosomes contain thousands of genes.
• - Genes are physically linked together on a
  chromosome.

41
B. Polyploidy

• - The occurrence of one or more extra sets of all
  chromosomes in an organism.
• - Rare in animals but occurs commonly in plants.
• - Produces new plant varieties

42
The End