1. Announcements SCI I, 407 M 12-3, 5:30-6:30; W 8-9, 5:30-6:30,
● Tutoring Center
SCI I, 407
M 12-3, 5:30-6:30; W 8-9, 5:30-6:30,
Th 8-12, 6-7; F 8-9
● MasteringBiology Assignment due Thursday 5/5 1

2. Phases of Mitosis Interphase B. ProphaseLM
(a)
(b)
(c)
(d)
Interphase B. Prophase
C. Metaphase D. Anaphase E. Telophase

3. Review of Terms A somatic cell A gametic cell (gamete)
Is a typical body cell
Has 46 chromosomes in a human
A gametic cell (gamete)
Is used for sexual reproduction
Usually termed eggs and sperm
Haploid – cell or organism that contains one complete set of chromosomes
Diploid - cell or organism that contains two complete sets of chromosomes

4. Review of Terms Autosome Sex chromosome
Chromosome that is not directly involved in determining the sex of an organism
Sex chromosome
A chromosome that determines whether an individual is male or female
Female
Somatic
cells
Male 44  XY XX

5. Meiosis
Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis. 5

6. Meiosis Homologous chromosomes separate. Chromosomes duplicate. Sister
chromatids
separate.
Pair of homologous
chromosomes in
diploid parent cell
Duplicated pair of
homologous
chromosomes
Sister
chromatids
INTERPHASE BEFORE MEIOSIS
MEIOSIS I
MEIOSIS II 6

7. Crossing over In crossing over:
Prophase I
of meiosis
Duplicated pair of
homologous
chromosomes
In crossing over:
Homologous chromosomes exchange genetic information
Genetic recombination,
the production of gene combinations different from those carried by parental chromosomes, occurs
Homologous chromatids
exchange corresponding
segments.
Chiasma, site of
crossing over
Metaphase I
Spindle
microtubule
Sister chromatids
remain joined at their
centromeres.
Metaphase II
Gametes
Recombinant
chromosomes
combine genetic
information from
different parents.
Recombinant chromosomes

8. Meiosis Cross over: How do we account for genetic variation?
*Independent assortment *Crossing over *Random fertilization
Independent Assortment: 8

9. Mitosis and Meiosis 9

10. Errors in Meiosis NONDISJUNCTION IN MEIOSIS I
NONDISJUNCTION IN MEIOSIS II
Meiosis I
Nondisjunction:
Pair of homologous
chromosomes fails
to separate.
Meiosis II
Nondisjunction:
Pair of sister
chromatids
fails to separate.
Gametes
Number of
chromosomes
n  1
n  1
n – 1
n – 1
n  1
n – 1 n n
Abnormal gametes
Abnormal gametes
Normal gametes

11. Errors in Meiosis Down Syndrome: Is also called trisomy 21
Is a condition in which an individual has an extra chromosome 21
Affects about one out of every 700 children

12. Genetics Genetics is the scientific study of heredity.
Heredity is the transmission of traits from one generation to the next. 12

13. Genetics Gregor Mendel •Worked in the 1860s
•Was the first person to analyze patterns of inheritance
•Deduced the fundamental principles of genetics 13

14. Genetics Mendel studied garden peas because they: •Easy to grow
Removed
stamens
from purple
flower.
White
Stamens
Purple
Transferred pollen from
stamens of white flower
to carpel of purple
Parents
(P)
Carpel
Offspring
(F1)
Pollinated carpel
matured into pod.
Planted seeds
from pod.
Mendel studied garden peas because they:
•Easy to grow
• Come in many readily distinguishable varieties
• Easily manipulated
• Can self-fertilize 14

15. Genetics
A character is a heritable feature that varies among individuals.
A trait is a variant of a character.
Each of the characters Mendel studied occurred in two distinct forms. 15

16. Genetics P Generation (true-breading parents) Purple flowers
White flowers
F1 Generation
All plants have
purple flowers
Fertilization
among F1 plants
(F1  F1)
F2 Generation 3 4 1 4
of plants
have purple flowers
of plants
have white flowers 16

17. Genetics Mendel’s hypotheses (to explain his results)
*genes and alleles
Mendel’s hypotheses (to explain his results)
1. Alternative versions of genes (alleles) account for variation in inherited characters.
2. For each character, an organism inherits two alleles, one from each parent. 17

18. Genetics
3. If two alleles differ, one is dominant, the other recessive
4. The two alleles for each character segregate (separate) during gamete production. P: X
DD dd
Tall
Dwarf
F1 – all Tall
Tall Dd
Mendel’s Law of Segregation 18

19. Genetics
A Punnett Square predicts the results of a genetic cross between individuals of known genotype
Tall
Dwarf P: X
DD dd
Gamete formation: D D d d d d
*genotype
*phenotype
4/4 are Dd
4/4 are Tall D D d D d
*Homozygous
*Heterozygous D D d D d 19

20. Genetics
Dihybrid cross- A genetic cross between two individuals involving two characters
Example: P1
yellow, round
green, wrinkled X
GW GW GW GW gw
GGWW
ggww F1
All yellow, round
GgWw 20

21. GW Gw gW gw F1 GW X Gw gW GgWw gw F2 All yellow, round
3/16 yellow, wrinkled
3/16 green, round
1/16 green, wrinkled
9:3:3:1 Phenotypic ratio; Genotypic ratio as follows:
1/16 GGWW, 2/16 GGWw, 2/16 GgWW, 4/16 GgWw
1/16 GGww, 2/16 Ggww
1/16 ggWw, 2/16 ggWw
1/16 ggww 21

22. Genetics Mendelian inheritance is based on probability
Example- coin toss
*1/2 chance landing heads B b
Female gametes
Male gametes
Formation of sperm
Bb male
Formation of eggs
Bb female
F2 Genotypes
F1 Genotypes
(  ) 1 2 4
*Each toss is an independent event
*Coin toss, just like the distribution of alleles into gametes
*The rule of multiplication – determines the chance that two or more independent events will occur together
½ x ½ = ¼ 22

23. Genetics: Pedigrees First generation (grandparents) Ff Ff ff Ff
Second generation
(parents, aunts, and
uncles) FF ff ff Ff Ff ff or Ff
Third generation
(brother and
sister) ff FF or Ff
Female Male
Attached
Free

24. Human Disorders

25. Variations in Mendel’s Laws
In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents.
F1 Generation RR rr
Gametes
P Generation
F2 Generation
Sperm
Red
White R r Rr
Pink
Eggs 1 2
Table 9.1 Some Autosomal Disorders in Humans

26. Variations in Mendel’s Laws
Hypercholesterolemia
Dangerously high levels of cholesterol in the blood.
Is a human trait that is incompletely dominant.
Heterozygotes have blood cholesterol levels about 2X normal.
Homozygotes have blood cholesterol levels about 5X normal. HH Hh hh
Homozygous
for ability to make
LDL receptors
Heterozygous
Homozygous
for inability to make
LDL receptors
GENOTYPE
LDL
LDL
receptor
PHENOTYPE
Cell
Normal
Mild disease
Severe disease

27. Variations in Mendel’s Laws
Multiple Alleles
Blood
Group
(Phenotype)
Genotypes
Red Blood Cells
Carbohydrate A
IAIA or
IAi A
Carbohydrate B
IBIB or
IBi B AB
IAIB O ii

28. Variations in Mendel’s Laws
Pleiotropy is the impact of a single gene on more than one character.
Pleiotropy
Multiple traits
(e.g., sickle-cell
disease)
Single
gene

29. Variations in Mendel’s Laws

30. Variations in Mendel’s Laws
Polygenic inheritance is the additive effects of two or more genes on a single phenotype.
Multiple genes
Polygenic
inheritance
Single trait
(e.g., skin color)

31. Variations in Mendel’s Laws
F1 Generation
P Generation
F2 Generation
Sperm
AABBCC
(very dark)
Eggs
aabbcc
(very light)
AaBbCc 1 8 64 6 15 20

32. Sex Linkage *1909 Thomas Hunt Morgan II III XY IV or XX
*Sex chromosomes
*Autosomes
Example: In Drosophila and all mammals
sex chromosomes designated as X and Y
XX=female
XY=male 32

33. Sex Linkage
Any gene located on a sex chromosome is called a sex-linked gene.
Most sex-linked genes are found on the X chromosome.