Chapter 11

1. Chapter 11 Genetics

2. Genetics • All living things have a set of characteristics inherited from its parent or parents • Genetics– the study of heredity • Trait – a specific characteristic, such as seed color • Genes – chemical factors (DNA segments) that control traits. Usually code for proteins • Alleles – forms of a gene, like T (tall) or t (short)

3. Gregor Mendel • Mendel was a monk in charge of the garden monastery • Mendel had stocks of plants that produced only tall, only short, only green seeds, and only yellow seeds • He studies cross-bred plants with different characteristics and studied the results • The offspring (F1) of crosses between parents (P) with different traits are called hybrids

4. Gregor Mendel

5. Gregor Mendel • All of the F1 generation had characteristic of only one parent (no blending) • Each characteristic was controlled by 1 gene with two contrasting forms, called alleles • Principle of dominance states that some alleles are dominant while others are recessive

6. Gregor Mendel

7. Gregor Mendel • He then crossed F1 plants to produce F2 plants • Recessive traits reappeared, roughly ¼ had the recessive traits • The two alleles of the F1 plant segregate from each other so that a gamete only has 1 copy of the gene • Each F1 plant gamete has either the dominant or recessive (tall or short)

8. Gregor Mendel

9. Mendel • Gregor Mendel concluded: • Inheritance is controlled by factors passed from one generation to the next. • Some alleles are dominant and others are recessive. • Segregation - the alleles (separate) during the formation of gametes. • Independent assortment - genes for different traits can segregate independently during the formation of gametes.

10. Punnett Squares • Punnett Squares – tool used to predict the probability of offspring with a certain trait or genotype. • Monohybrid cross – Punnett square with one trait, 4 squares.

11. Genetic Terms • Dominant – occurs in the phenotype if one allele is present, T • Recessive – must be homozygous to occur in the phenotype • Homozygous – having two identical alleles for a trait, TT or tt • Heterozygous – having two different alleles for a trait, Tt • Phenotype – physical characteristic, tall • Genotype – genetic makeup, TT or Tt

12. Monohybrid Cross

13. Dihybrid Cross • Since alleles can segregate independently, the inheritance of one trait doesn’t affect the inheritance of another (seed color and seed shape) • A dihybrid cross involves crossing two different traits of the F1 generation (both parents are heterozygous for both traits)

14. Dihybrid Cross

15. Complex Forms of Inheritance • Some alleles are neither dominant or recessive, and many traits are controlled by multiple alleles or multiple genes • Codominance– both alleles are present in the phenotype, the black and white chicken, blood types • Incomplete dominance – the alleles blend to produce the phenotype, red + white = pink

16. Blood Types: Codominance

17. Incomplete dominance

18. Complex Forms of Inheritance • Multiple alleles – more than 2 alleles are possible choices, although only 2 can be used at a time, ex. ABO blood groups, rabbit coat color • Polygenic traits – controlled by 2 or more genes, ex. skin color • Sometimes expression is also affected by the environment; height and flower color of a sunflower are affected by genes and climate, soil, and water availability

19. Multiple Alleles

20. Sex-linked • Genes that are located on sex chromosomes are said to be sex-linked genes • Since males only have 1 X chromosome, all X-linked alleles are expressed, even if recessive • For females, a recessive allele must be with another recessive to be expressed • Colorblindness and hemophilia is an example

21. Sex-linked

22. Chapter 14 Heredity

23. Human Heredity • A karyotype is a picture of chromosomes arranged in their pairs (46, 23 pairs in humans) Male Female

24. Human Heredity • All egg cells carry an X chromosome, half sperm cells carry an X, half a Y • Leads to half combined becoming either XY, or XX • Autosomes are non-sex chromosomes, labeled pairs 1-22 chromosomes • Sex chromosomes are the 23rd pair of chromosomes

25. Human Heredity • To study how traits are passed from generation to generation a pedigree chart is used • Males are squares • Females are circles • Shaded circle/squares have the trait • Horizontal lines represent marriage • Vertical lines connect parents to their offspring • White forelock (lock of hair just above the forehead) is dominant

26. Human Heredity

27. Human Heredity • Many disorders are caused by an autosomal recessive allele (disease is only apparent in the homozygous recessive condition) • Some disorders are expressed with only one allele (dominant), which means the disease is apparent in the heterozygous condition • Some disorders are caused by a codominant alleles

28. Human Heredity

29. Human Heredity • Cystic fibrosis leads to serious digestive problems • Thick, heavy mucus clogs lungs and breathing passages • Since it is recessive, must have 2 alleles to be affected • Sickle cell disease leads to bent/twisted shape of RBCs (can clog in capillaries) • Heterozygous individuals are generally healthy and more resistant to malaria

30. Chromosomal Disorders • Down syndrome (trisomy 21) • Nondisjunction occurs when homologous chromosomes don’t separate during meiosis-leads to abnormal number of chromosomes • 3 copies of chromosome 21 • Mild to severe mental disability, and higher susceptibility to many diseases • Sex chromosome nondisjunction • Turner syndrome (X): sterile • Klinefelter’s syndrome (XXY): generally sterile