Genetics Genetics is the scientific study of heredity and variation.

Genetics In asexual reproduction: Single-celled organisms reproduce by simple cell division There is no fertilization of an egg by a sperm Asexual Reproduction FUNCTIONS OF CELL DIVISION Sea stars LM Amoeba African Violet

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

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

Genetics Removed stamens from purple flower. White Stamens Purple Transferred pollen from stamens of white flower to carpel of purple flower. Parents (P) Carpel Offspring (F 1 ) 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

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.

*P - parental generation *F 1 – first filial generation *F 2 – second filial generation -Example: X TallDwarf P F 1 – all Tall Tall F2F2 Genetics

Mendel’s hypotheses (to explain his results) *genes and alleles 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. Genetics

3. If two alleles differ, one is dominant, the other recessive X TallDwarf P: DD dd F 1 – all Tall Tall Dd 4. The two alleles for each character segregate (separate) during gamete production. Mendel’s Law of Segregation Genetics

A Punnett Square predicts the results of a genetic cross between individuals of known genotype Ddd TallDwarf P: DD dd X Gamete formation: D *genotype *phenotype *Homozygous *Heterozygous DDddDdDdDdDd 4/4 are Dd 4/4 are Tall

Genetics

Dihybrid cross- A genetic cross between two individuals involving two characters GGWWggww Example: P1P1 yellow, roundgreen, wrinkled X GW GW gw GgWw Genetics F1F1 All yellow, round

F1F1 GgWw F1F1 All yellow, round GgWw X F2F2 9/16 yellow, round 3/16 yellow, wrinkled 3/16 green, round 1/16 green, wrinkled GW Gw gW gw gW GW gw Gw 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

Mendelian inheritance is based on probability Example- coin toss *1/2 chance landing heads *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 B B b B b b Female gametes B B B b b b Male gametes Formation of sperm Bb male Formation of eggs Bb female F 2 Genotypes F 1 Genotypes (  ) Genetics

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

Human Disorders

F 1 Generation RRrr Gametes P Generation F 2 Generation Sperm Gametes Red White R r Rr Pink R r R r R r RRRr rr Rr Eggs Variations in Mendel’s Laws In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents.

Homozygous for ability to make LDL receptors Severe disease Mild disease Cell Normal LDL receptor LDL Homozygous for inability to make LDL receptors Heterozygous HH Hh hh GENOTYPE PHENOTYPE 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. Variations in Mendel’s Laws

Blood Group (Phenotype) Genotypes Red Blood Cells O A B AB ii IAIBIAIB I B or I B i I A or I A i Carbohydrate A Carbohydrate B Variations in Mendel’s Laws Multiple Alleles

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

Variations in Mendel’s Laws

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

F 1 Generation P Generation F 2 Generation Sperm AABBCC (very dark) Eggs aabbcc (very light) AaBbCc

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

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