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Two copies of each autosomal gene affect phenotype (physical). Mendel studied autosomal gene traits, like hair texture. Autosome – chromosome with genes.

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Presentation on theme: "Two copies of each autosomal gene affect phenotype (physical). Mendel studied autosomal gene traits, like hair texture. Autosome – chromosome with genes."— Presentation transcript:

1 Two copies of each autosomal gene affect phenotype (physical). Mendel studied autosomal gene traits, like hair texture. Autosome – chromosome with genes not related to sex of organism (body cells)

2 –Carrier – has an allele for a trait or disease that is not expressed. –Carrier does not have disease symptoms but can pass it on to offspring. (dominant) Dominant allele disorders are rare. Huntington’s disease is an example of a disease caused by a dominant allele.

3 . Genes on sex chromosomes are called sex-linked genes. –Y chromosome - male characteristics. –X chromosome - genes affects many traits. Males can pass on X or Y Females only pass on X

4 Who determines the sex of the offspring? XX XY Sperm Body Cell XX X X X Y Y X X X 1female:1male Father – he can provide an X or Y chromosome Egg

5 Males have an XY genotype. –All of a male’s sex-linked genes are expressed. –Males have no second copies of sex-linked genes –Y chromosome is much smaller

6 Females have an XX genotype. X chromosome inactivation -randomly “turns off” one X chromosome. Why are males more likely than females to have genetic disorders? All sex-linked genes are expressed, even recessive. Females have a backup X chromosome.

7 Color blindness is a problem in which red or green look like shades of gray or other colors. The gene is carried on the X chromosome and is a recessive trait. X C X C X C X c X C Y X c Y XCXC XcXc XCXC Y X C X C = normal female X C X c = female, normal vision (carrier) X C Y = normal vision male X c Y = color blind male

8 Some traits are neither totally dominant nor totally recessive. Incomplete dominance - when neither gene is totally dominant to the other - Heterozygous phenotype is intermediate between the two homozygous phenotypes –Example: White flowers and red flowers produce pink flowers

9 Codominance Sickle Cell Anemia R = Round blood cells R’ = Sickle Cells RR RR’ R’R’ R R’ R Disease in which the body makes sickle- shaped red blood cells. Sickle-shaped cells don’t move easily through your blood vessels. They’re stiff and sticky and tend to form clumps and get stuck in the blood vessels. RR = normal blood RR’ = some sickle cells, some normal cells R’R’ = has sickle cell anemia

10 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. Example – red and white flower produce a flower with BOTH colors

11 Polygenic traits are produced by two or more genes. Order of dominance: brown > green > blue.

12 Epistatic gene - can interfere with the expression of all other genes. Mice have 5 genes that control fur color. 2 genes for general color 1 for shading 1 for spots 1 epistatic gene for color that overrules all other genes

13 Height is an example of a phenotype strongly affected by the environmental factors such as early nutrition and health care. The sex of sea turtles depends on both genes and the environment. Warm eggs develop into females Phenotype is a combination of genotype and environment.

14 Gene linkage was explained through fruit flies. Morgan found that linked traits are on the same chromosome. Traits can be inherited as a group. Chromosomes, not genes, assort independently during meiosis. Wild type Mutant

15 Linked genes are not inherited together every time. Chromosomes exchange homologous genes during meiosis.

16 Linkage maps – map of location of genes on a chromosome. The closer together two genes are, the more likely they will be inherited together. Cross-over frequencies are related to distances between genes.

17 Cross-over frequencies can be converted into map units. – gene A and gene B cross over 6.0 percent of the time – gene B and gene C cross over 12.5 percent of the time – gene A and gene C cross over 18.5 percent of the time

18 Human genetics follows the patterns seen in other organisms. The basic principles of genetics are the same in all sexually reproducing organisms. –Inheritance of many human traits is complex. –Single-gene traits are important in understanding human genetics.

19 Females can carry sex-linked genetic disorders. Males (XY) express all of their sex linked genes. Expression of the disorder depends on which parent carries the allele and the sex of the child. X chromosome carries about 1100 genes while the Y carries about 250

20 Pedigree - chart for tracing genes in a family. Phenotypes are used to infer genotypes on a pedigree. Autosomal genes show different patterns on a pedigree than sex-linked genes. Widow’s peak: W = widow’s peak w = non widow’s peak

21 If the phenotype is more common in males, the gene is likely sex-linked. Colorblindness: M = normal vision m = colorblindness

22 Several methods help map human chromosomes. Karyotype - a picture of all chromosomes in a cell. X Y

23 Karyotypes can show changes in chromosomes. –deletion of part of a chromosome or loss of a chromosome –large changes in chromosomes –extra chromosomes or duplication of part of a chromosome


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