14 1 Human Heredity. Week 8 vocab Chapter 14

Transcription

1 Week 8 vocab Chapter 14 Vocab 1. Karyotype 5. sex-linked gene 2. sex chromosome 6. nondisjunction 3. pedigree 7. DNA fingerprinting 4. Polygenic 1 of 43

2 Biology Biology 2 of 43

3 14-1 Human Heredity 3 of 43

4 Human Chromosomes Human Chromosomes Cell biologists analyze chromosomes by looking at karyotypes. Cells are photographed during mitosis. Scientists then cut out the chromosomes from the photographs, and group them together in pairs. A picture of chromosomes arranged in this way is known as a karyotype. 4 of 43

5 Human Chromosomes Human Karyotype 5 of 43

6 Human Chromosomes Humans have 46 chromosomes 2 of these are known as sex chromosomes, because they determine if you are a male or female. Females have two copies of the X chromosome. Males have one X chromosome and one Y chromosome. The remaining 44 chromosomes are known as autosomal chromosomes, or autosomes. 6 of 43

7 A normal karyotype shows 23 pairs of chromosomes 22 autosomes and 1 pair of sex chromosomes XX, or XY Is this a male or female? (hint: the sex chromosomes are below chromosome 15) 7 of 43

8 Human Chromosomes How is sex determined? 8 of 43

9 Human Chromosomes Each parent passes down one allele for the sex trait. Females will pass down one of their X chromosome and males can pass down an X or Y. There is an equal chance of having a boy or girl. It ultimately depends on which alelle the father contributes. 9 of 43

10 Human Traits Pedigree Charts A pedigree chart shows the relationships within a family. Genetic counselors analyze pedigree charts to infer the genotypes of family members. 10 of 43

11 Human Traits A horizontal line connecting a male and a female represents a marriage. A shaded circle or square indicates that a person expresses the trait. A circle represents a female. A square represents a male. A vertical line and a bracket connect the parents to their children. A circle or square that is not shaded indicates that a person does not express the trait. 11 of 43

12 Sex-Linked Genes The X chromosome and the Y chromosomes determine sex. Genes located on these chromosomes are called sex-linked genes. More than 100 sex-linked genetic disorders have now been mapped to the X chromosome. 12 of 43

13 X Chromosome The Y chromosome is much smaller than the X chromosome and appears to contain only a few genes. Duchenne muscular dystrophy Melanoma X-inactivation center X-linked severe combined immunodeficiency (SCID) Colorblindness Hemophilia Y Chromosome Testis-determining factor 13 of 43

14 Sex-linked disorders more common in males than in females. 14 of 43

15 For a recessive disease to be expressed in females, there must be two copies of the allele, one on each of the two X chromosomes. Males have just one X chromosome. All X- linked alleles are expressed in males, even if they are recessive. 15 of 43

16 Examples of Sex-linked Disorders caused by recessive alleles 1. Colorblindness-difficulty distinguishing color 2. Hemophelia- blood clotting disorder 3. Muscular Dystrophy-weakening and loss of skeletal muscle. 16 of 43

17 What is Nondisjunction and what problems does it cause? The most common error in meiosis occurs when homologous chromosomes fail to separate. This is known as nondisjunction, which means, not coming apart. 17 of 43

18 If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result. 18 of 43

19 Nondisjunction During meiosis The 4 gamete cells should be haploid. Instead, 2 cells have extra chromosomes, and 2 cells are missing chromosomes. 19 of 43

20 Down Syndrome If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of a chromosome. Down syndrome involves three copies of chromosome of 43

21 Down syndrome produces mild to severe mental retardation. This karyotype shows a female with 3 copies of chromosome 21 (she should only have 2 copies) How do we know she s a female? (two X chromosomes) Down Syndrome Karyotype 21 of 43

22 In females, nondisjunction can lead to Turner s syndrome. A female with Turner s syndrome usually inherits only one X chromosome ( 45 chromosomes total). Women with Turner s syndrome are sterile. Only one x chromosome 22 of 43

23 In males, nondisjunction causes Klinefelter s syndrome (has 47 chromosomes). The extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing. 23 of 43