Honors Biology Ch. 10

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Honors BiologyCh. 10

• Sexual Reproduction and Genetics

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I. Meiosis

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

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

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

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Human Chromosomes(23 homologous pairs)
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C. Haploid

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

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D. Process of Meiosis

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

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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) The homologous chromosomes separate during
  anaphase I.
• c) 2 cells are produced that contain 1 replicated
  chromosome from each homologous pair.

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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
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Crossing Over
Purple
Long
SisterChromatids
Purple
Long
red
round
SisterChromatids
red
round
old combination
new combination
new combination
old combination
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Chiasmata
Crossing-over in a tetrad of a grasshopper. Each
cross-over is called a chiasma. This example
shows 5 chiasmata.
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2. Meiosis II

• a) similar to mitosis but DNA replication does
  not occur before division
• b) Sister chromatids separate during anaphase II.
• c) 4 haploid daughter cells are produced

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Meiosis II
FourHaploidCells
Prophase II
Anaphase II
Metaphase II
Telophase II
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Spermatogenesis
Oogenesis
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E. Importance of Meiosis

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

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

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

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The Results of Crossing over During Meiosis
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3. Random Fertilization

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

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II. Mendels Laws of Heredity

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

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Early Idea about Genetics
Homunculus
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A. Gregor Mendel

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

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B. Mendels Experiments

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

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- easy to control pollinate
Pistil(female)produceseggs
Stamens(male)producepollen
Pea Flower
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- seven distinct, inherited traits
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• 2. Used math and statistics to support theories
• 3. Published results in 1859- rejected by
  academic peers- in 1900 his work was rediscovered

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P
F1
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F1
F2
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III. Principles of Heredity

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

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B. Principle of Dominance and Recessiveness

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

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C. Law of Segregation

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

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

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

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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

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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
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D. Principle of Independent Assortment

• - alleles separate randomly during meiosis

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IV. Applying Mendels Principles

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

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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
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• Cystic Fibrosis F Normal
• f cystic fibrosis
• 1 out of 25 are heterozygous in UK
• Odds of any heterozygous man and woman marrying
• 1/25 x 1/25
• Odds of a heterozygous man and woman having a
  child with cystic fibrosis
• 1/625 x 1/4

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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
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V. Gene Linkage and Polyploidy

• A. Gene Linkage
• - Chromosomes contain thousands of genes.
• - Genes are physically linked together on a
  chromosome.
• - During crossing over this linkage can be
  broken temporarily.
• - Frequency of crossing over can be used to
  make chromosome maps.

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V. Gene Linkage and Polyploidy

• A. Gene Linkage

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V. Gene Linkage and Polyploidy

• A. Gene Linkage

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B. Polyploidy

• - The occurrence of one or more extra
  sets of all chromosomes in an organism.

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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

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A Sample of Agricultural Crops That Are Polyploid
Corn, 4n 20
Banana, 3n 33
Canola oil, 4n 38
Potatoes, 4n 48
Bread wheat, 6n 42
Rope from sisal, 5n 180
Coffee beans, 4n 44
Cotton, 4n 52
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The Evolution of Wheat
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The End
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• 3. When an event can happen in more than one
  combination, the probability of the event is the
  sum of the probability of each.

What are the odds of getting a head and a tail
any order?
OR
1/4
1/4
1/2