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7.1 Chromosomes and Phenotype

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Presentation on theme: "7.1 Chromosomes and Phenotype"— Presentation transcript:

1 7.1 Chromosomes and Phenotype
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 7.1 Chromosomes and Phenotype
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 7.1 Chromosomes and Phenotype
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 7.1 Chromosomes and Phenotype
Who determines the sex of the offspring? Father – he can provide an X or Y chromosome Egg X X X XX XX XY XX X X Body Cell X XY Y Y Sperm Body Cell 1female:1male

5 7.1 Chromosomes and Phenotype
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 7.1 Chromosomes and Phenotype
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 Complex Patterns of Inheritance
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. XC Xc XCXC XCXc XCY XcY XC XCXC = normal female XCXc = female, normal vision (carrier) XCY = normal vision male XcY = color blind male Y

8 Complex Patterns of Inheritance
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 RR RR’ R’R’ R = Round blood cells R’ = Sickle Cells
Sickle Cell Anemia R = Round blood cells R’ = Sickle Cells 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 . R R’ RR RR’ R’R’ R RR = normal blood RR’ = some sickle cells, some normal cells R’R’ = has sickle cell anemia R’

10 Complex Patterns of Inheritance
Codominant - alleles will both be completely expressed. Example – red and white flower produce a flower with BOTH colors Codominant alleles are neither dominant nor recessive. The ABO blood types result from codominant alleles. Many genes have more than two alleles.

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

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

14 Gene Linkage and Mapping
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 Gene Linkage and Mapping
Linked genes are not inherited together every time. Chromosomes exchange homologous genes during meiosis.

16 Gene Linkage and Mapping
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 Gene Linkage and Mapping
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 and Pedigrees
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 Gene Linkage and Mapping
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 Gene Linkage and Mapping
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 Gene Linkage and Mapping
If the phenotype is more common in males, the gene is likely sex-linked. Colorblindness: M = normal vision m = colorblindness

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

23 Gene Linkage and Mapping
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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