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Announcements SCI I, 407 M 12-3, 5:30-6:30; W 8-9, 5:30-6:30,

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Presentation on theme: "Announcements SCI I, 407 M 12-3, 5:30-6:30; W 8-9, 5:30-6:30,"— Presentation transcript:

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. Prophase
LM (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

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.

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