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Chapter 14 Human Genetics. Human Genes and Chromosomes 31 thousand genes located over 46 chromosomes Autosomes – 22 pairs (44 total) Sex Chromosomes –

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Presentation on theme: "Chapter 14 Human Genetics. Human Genes and Chromosomes 31 thousand genes located over 46 chromosomes Autosomes – 22 pairs (44 total) Sex Chromosomes –"— Presentation transcript:

1 Chapter 14 Human Genetics

2 Human Genes and Chromosomes 31 thousand genes located over 46 chromosomes Autosomes – 22 pairs (44 total) Sex Chromosomes – 1 pair (2 total) –XX = female –XY = male –Some genes are located on the sex chromosomes….they are called “sex- linked”

3 Sex Determination: - will a child be male or female? X X Y X XX XY XX XY X X Y X x x eggssperm female (XX) male (XY)

4 Men show sex-linked traits more often… Why?

5 Sex-linked genes…aka: X-linked genes A.Hemophilia B.Colorblindness C.Duchenne Muscular Dystrophy **Must take into consideration the X and the Y chromosomes when doing these problems **We refer to X-linked genes with superscripts ex: X H X h =female carrier of hemophilia X h X h =female hemophiliac X h Y =male hemophiliac Why are most of these genes located on the X chromosome?

6 Completing sex-linked Punnett Squares:

7 Hemophilia – The X chromosome carries genes that help control blood clotting. – In hemophilia, a protein necessary for normal blood clotting is missing. – Hemophiliacs can bleed to death from cuts and may suffer internal bleeding if bruised.

8 Practice Problem: What are the chances for a mother that is a carrier for hemophilia and a hemophiliac father to have hemophiliac children?

9 Father (normal vision) Colorblind Normal vision Mother (carrier) Daughter (normal vision) Son (normal vision) Daughter (carrier) Son (colorblind) Male Female Go to Section: Color blindness: Three human genes associated with color vision are located on the X chromosome. In males, a defective version of any one of these genes produces colorblindness.

10 Duchenne muscular dystrophy – Duchenne muscular dystrophy is a sex-linked disorder that results in the weakening and loss of skeletal muscle. – It is caused by a defective version of the gene that codes for a muscle protein.

11 Pedigrees and sex-linked traits: Terms to know: Normal= unaffected with disease  unshaded in pedigrees Affected= has disease  fully shaded in pedigrees Square= male Circle= female

12 Practice Problem: This pedigree shows the inheritance of hemophilia: Find the phenotypes for #1, #2, and #4 If #5 marries a woman who is heterozygous for the hemophiliac gene, X H X h, what are their chances for having children with hemophilia?

13 Genetic Disorders: Autosomal Caused by Recessive Alleles Recessive disorders only appear if two recessive alleles are present. Albinism Cystic fibrosis Galactosemia

14 Cystic Fibrosis Sufferers of cystic fibrosis produce a thick, heavy mucus that clogs their lungs and breathing passageways. The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

15 Genetic Disorders: Autosomal Caused by Dominant Alleles : Dominant disorders are caused by dominant alleles, so only one allele is needed for the disease to show. Achondroplasia Huntington’s Disease Hypercholesterolemia

16 Genetic Disorders: Chromosomal  Caused by Nondisjunction – Down Syndrome— Trisomy Chromosome 21 – Down syndrome produces mild to severe mental retardation. – It is characterized by: increased susceptibility to many diseases higher frequency of some birth defects Karyotype: picture of human chromosomes

17 Changes in Chromosome Number usually the result of Nondisjunction n + 1 n - 1 chromosome alignments at metaphase I nondisjunction at anaphase I alignments at metaphase II anaphase II

18 Nondisjunction in Sex C h r o m o s o m e s Turner’s Syndrome—Monosomy Sex Chromosome (X0) A female with Turner’s syndrome usually inherits only one X chromosome (karyotype 45,X). Women with Turner’s syndrome are sterile. Klinefelter’s Syndrome—Trisomy Sex Chromosome (XXY) The extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing.

19 Pedigree Analysis Technique to study patterns of human inheritance Visual representation of family history Several possible modes of inheritance are able to be identified: – Autosomal dominant traits – Autosomal recessive traits – Sex-linked traits

20 What information do we find in a pedigree? Male with “normal” traitFemale with “normal” trait Female affected Male affected Horizontal lines between a male and a female = marriage Vertical lines coming down from a marriage = offspring

21 Autosomal Dominant Appears in both sexes with equal frequency Can be passed on to the next generation by both males and females Does not skip a generation Ex: Huntington’s Disease

22 Autosomal Recessive Appears at equal frequency in both sexes. Only appears when the affected individual has received one allele from each parent Skips generations Ex: Cystic Fibrosis

23 Sex-linked more frequent in males trait tends to skip generations

24 MCAS practice question People who are tune deaf are unable to follow a rhythm. Scientists have evidence that tune deafness can be genetic. The pedigree below traces the inheritance of tune deafness in a family. Individuals in the pedigree are numbered. Scientists have analyzed the inheritance patterns for tune deafness and have concluded that tune deafness is caused by an autosomal dominant allele, T a.Provide evidence from the pedigree that shows that the tune deafness allele is autosomal dominant, not autosomal recessive. Explain. a.Identify the genotypes of individuals 5 and 6, and then draw the Punnett square for the cross of these two individuals.

25 CASE STUDY: ABO Blood Typing What inheritance patterns does human blood type demonstrate?

26 ABO Gene Determined by a single gene with 3 alleles, 2 of which are codominant Type A Blood (type A marker) – Makes antibody for B Type B Blood (type B marker) – Makes antibody for A Type AB Blood (both A & B markers) – Makes no antibodies Type O Blood (neither marker) – Makes antibodies for A and B

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28 Risks of Blood Transfusions Donor RBCs may not have the same kind of recognition molecules (“markers”) on their surfaces as Recipient RBCs Potential Result: – Agglutination, a defense response.  CLUMPING Antibodies act against foreign cells and cause them to clump together Antibodies are produced against antigens NOT present on RBCs

29 When does agglutination occur? Type A – antibodies ignore A marker, attack B markers Type B – antibodies ignore B marker, attack A markers Type AB – antibodies ignore both forms Type O – antibodies attack both A and B markers

30 Phenotype (Blood Type) Genotype Antigen on Red Blood Cell Safe Transfusions To From Go to Section: Blood Transfusions and Agglutination

31 Blood Typing in Forensics Can be used to determine the blood type of a potential suspect in a crime Test uses two solutions each containing antibodies to type A and type B antigens. – Solution 1: Anti-A; when mixed with type A blood will cause it to form clumps. – Solution 2: Anti-B; when mixed with type B blood will cause it to form clumps. If blood clumps under contact with both Anti-A and Anti-B, then it is type AB O blood does not clump

32 Rh Gene Rh marker determined by a single gene with 2 alleles – Rh+ allele=Dominant=markerpresent – Rh- allele=recessive=marker not present


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