6.6 Meiosis and Genetic Variation. KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

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1 6.6 Meiosis and Genetic Variation KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

2 6.6 Meiosis and Genetic Variation! Sexual reproduction creates unique combinations of genes. Sexual reproduction creates unique combination of genes. independent assortment of chromosomes in meiosis random fertilization of gametes Unique phenotypes may give a reproductive advantage to some organisms.

3 6.6 Meiosis and Genetic Variation! Crossing over during meiosis increases genetic diversity. Crossing over is the exchange of chromosome segments between homologous chromosomes. occurs during prophase I of meiosis I results in new combinations of genes

4 6.6 Meiosis and Genetic Variation Chromosomes contain many genes. The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over. Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage. Genetic linkage allows the distance between two genes to be calculated.

5 S-B-8-1_Non-Mendelian Heredity PowerPoint 6.6 Meiosis and Genetic Variation! Linked Traits When the loci of two genes are located close together on the same chromosome Red hair, freckles, and fair skin are linked.

6 7.1 Chromosomes and Phenotype KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

7 7.1 Chromosomes and Phenotype! Two copies of each autosomal gene affect phenotype. Mendel studied autosomal gene traits, like hair texture.

8 7.1 Chromosomes and Phenotype Mendel s rules of inheritance apply to autosomal genetic disorders. A heterozygote for a recessive disorder is a carrier. Disorders caused by dominant alleles are uncommon. (dominant)

9 7.1 Chromosomes and Phenotype! Males and females can differ in sex-linked traits. Genes on sex chromosomes are called sex-linked genes. Y chromosome genes in mammals are responsible for male characteristics. X chromosome genes in mammals affect many traits.

10 7.1 Chromosomes and Phenotype Male mammals have an XY genotype. All of a male s sexlinked genes are expressed. Males have no second copies of sex-linked genes.

11 7.1 Chromosomes and Phenotype Female mammals have an XX genotype. Expression of sex-linked genes is similar to autosomal genes in females. X chromosome inactivation randomly turns off one X chromosome.

12 S-B-8-1_Non-Mendelian Heredity PowerPoint 7.1 Chromosomes and Phenotype! Sex-Linked Traits Genes located on a sex (X or Y) chromosome XX & XY Some forms of hemophilia Red-green colorblindness

13 S-B-8-1_Non-Mendelian Heredity PowerPoint Barr Bodies The inactive X chromosome found in female (XX) somatic cells Not found in normal males (XY). Explains calico coloring in cats. The nucleus of a cell. The arrow is pointing to the inactive X chromosome, the Barr Body.

14 S-B-8-1_Non-Mendelian Heredity PowerPoint 7.1 Chromosomes and Phenotype! Calico Cats

15 S-B-8-1_Non-Mendelian Heredity PowerPoint 7.1 Chromosomes and Phenotype! Solving Sex-Linked Problems A woman who is a carrier for red-green colorblindness marries a man with normal sight. What percent of the male and female children will be red-green colorblind or carriers? STEP 1: XX' XY STEP 2: X, X' X, Y STEP 3: STEP 4: STEP 5: X X XX Y XY X' XX' X'Y STEP 6: 50% Normal 50% Carriers 50% Normal 50% Colorblind

16 S-B-8-1_Non-Mendelian Heredity PowerPoint 7.1 Chromosomes and Phenotype! THINK-PAIR-SHARE 1 2 Wild Type Homozygous Heterozygous 1. Is the trait sex-linked? How do you know? 2. How could we tell if female #5 is heterozygous if she never has children? 3. What are the expected phenotypic ratios from a cross between #3 & #7?

17 7.2 Complex Patterns of Inheritance! Phenotype can depend on interactions of alleles. In incomplete dominance, neither allele is completely dominant nor completely recessive. Heterozygous phenotype is intermediate between the two homozygous phenotypes Homozygous parental phenotypes not seen in F1 offspring

18 S-B-8-1_Non-Mendelian Heredity PowerPoint Incomplete Dominance Heterozygotes look different from a homozygotes Blending of phenotypes RR x R I R I RR I

19 7.2 Complex Patterns of Inheritance Codominant alleles will both be completely expressed. Codominant alleles are neither dominant nor recessive. The ABO blood types result from codominant alleles. Many genes have more than two alleles.

20 Codominance: Both alleles of a gene pair are expressed. Example: Human Blood Types Human blood type is determined by codominant alleles. There are three different alleles: I A, I B, and i. The I A and I B alleles are codominant, and the i allele is recessive. The possible human phenotypes for blood group are type A, type B, type AB, and type O. Type A and B individuals can be either homozygous (I A I A or I B I B, respectively), or heterozygous (I A i or I B i, respectively). Type O is I O I O. S-B-8-1_Non-Mendelian Heredity PowerPoint

21 S-B-8-1_Non-Mendelian Heredity PowerPoint THINK-PAIR-SHARE 1. Distinguish between incomplete dominance and codominance. 2. How many phenotypes are seen when codominance is possible? 3. Red color (R) in snapdragons shows incomplete dominance to white snapdragons (R I ). The heterozygotes are pink. If pink snap dragons are crossed with a white snapdragon, what are the genotypic/ phenotypic ratios? R R I R I RR I R I R I

22 S-B-8-1_Non-Mendelian Heredity PowerPoint Problems with Multiple Alleles A woman with type O blood marries a man with type AB blood. What are the possible blood types that a child of theirs could inherit? STEP 1: ii I A I B STEP 2: i I A, I B STEP 3: STEP 4: STEP 5: i I A I A i I B I B i STEP 6: There s a 50% chance that their baby will be Type A or Type B.

23 S-B-8-1_Non-Mendelian Heredity PowerPoint 7.2 Complex Patterns of Inheritance! THINK-PAIR-SHARE Black fur (B Bl ) is completely dominant to brown fur in rabbits, but brown fur (B Br ) is dominant to white (b). A hybrid brown doe (B Br b) is crossed with a hybrid black buck (B Bl b). What are the expected phenotypes of the offspring? Ratios?

24 7.2 Complex Patterns of Inheritance! Many genes may interact to produce one trait. Polygenic traits are produced by two or more genes. Order of dominance: brown > green > blue.

25 S-B-8-1_Non-Mendelian Heredity PowerPoint Polygenic Inheritance Poly-many genic-gene More than one gene on more than one loci or on more than one chromosome. Give the appearance of gradation Hair & skin color Height Body size

26 7.2 Complex Patterns of Inheritance! The environment interacts with genotype. Phenotype is a combination of genotype and environment. The sex of sea turtles depends on both genes and the environment Height is an example of a phenotype strongly affected by the environment.