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Inheritance Principles and Human Genetics BioH - Chapter 11.

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Presentation on theme: "Inheritance Principles and Human Genetics BioH - Chapter 11."— Presentation transcript:

1 Inheritance Principles and Human Genetics BioH - Chapter 11

2 Genetics Vocabulary Review Genes – units of information about heritable traits Homologous chromosomes – similar chromosomes received from male and female that line up next to each during MetaphaseI in meiosis Alleles – different forms of a gene Locus – location on a chromosome where specific genes are found Linkage – when genes on a chromosome stay together even during crossing-over Genetic recombination – the recombining of genes as a result of crossing-over

3 Chromosomes Thomas Hunt Morgan Thomas Hunt Morgan –Studied fruit flies –Found X and Y chromosomes

4 Karyotypes Karyotyping is a process that allows chromosomes to be presented in an orderly, easily compared manner

5 Sex chromosomes (X, Y) Sex chromosomes (X, Y) –Contain genes that determine the sex (gender) of an individual Autosomes Autosomes –Not directly involved in determining the sex of an individual –Different organisms, different number XY

6 Sex determination –Sperm has equal chance of receiving X or Y –Egg only receives X XX – female XX – female XY - male XY - male –Totally RANDOM process Sex-determination Region Y (SRY) Sex-determination Region Y (SRY) –Found in mammalian Y chromosome –Gene codes protein to cause gonads to develop testes gonads to develop testes

7 Gene location Sex-linked Sex-linked –Traits coded for by an allele on a sex chromosome –Could be on X or Y chromosome –More X-linked genes because X is much larger –If male carries a recessive allele on the X chromosome, it will exhibit the trait Ex. Hemophilia (blood disorder) Ex. Hemophilia (blood disorder)

8 Linked genes Linked genes –Traits that are inherited together –Makes a linkage group –This happens because they are found close to each other in the same chromosome and not as easily genetically recombined by crossing- over

9 Chromosome Map A diagram that shows the linear order of genes on a chromosome A diagram that shows the linear order of genes on a chromosome Map unit – frequency of crossing over of 1%. Map unit – frequency of crossing over of 1%.

10 Mutations Germ-cell mutations Germ-cell mutations –Occur in gametes (may not be expressed until offspring) Somatic-cell mutations Somatic-cell mutations –Occur in body cells –May affect organs Skin cancer and leukemia Skin cancer and leukemia –Lethal mutations Cause death, often before birth Cause death, often before birth

11 Inheritance of Traits Pedigrees Pedigrees –A diagram showing how a trait is inherited over several generations

12 Russian Royal Family & hemophilia Genetic abnormality – rare, uncommon trait version Genetic disorder – inherited condition causing medical disorders Syndrome – recognized set of disorders that characterize a disorder

13 Patterns of Inheritance If a trait is If a trait is –Autosomal Appears in both sexes equally Appears in both sexes equally Dominant Dominant –Every individual with the trait will have parents with the trait BB or Bb (dominant trait will show) BB or Bb (dominant trait will show) bb (recessive trait will show) bb (recessive trait will show) Recessive Recessive –1, 2, or no parent with the trait –Bb X Bb will not show mutation but can produce children for the recessive allele (bb) –Bb (carrier)

14 Genetic Trait and Disorders Single-Allele traits Single-Allele traits –Controlled by a single allele of a gene –More 200 human traits –Huntingtons disease Forgetfulness and irritability Forgetfulness and irritability

15 Gene Inheritance & Disorders Polygenic Inheritance Polygenic Inheritance –Traits are influence by more than one gene Skin color Skin color –3 to 6 genes –Genes control amount of melanin Eye color, height, hair color Eye color, height, hair color

16 Complex characters Complex characters –Influenced both by environment and genes –Skin color, breast cancer, height

17 Multiple Alleles Multiple Alleles –Genes with 3 or more alleles –ABO blood groups –I A, I B, and I –I A and I B are codominant Codominance Codominance –Both alleles are expressed –I A I B is type AB

18 Incomplete dominance Incomplete dominance –Trait that is displayed is intermediate between the two parents. –Hair type Curly (CC) X Straight (cc)= Wavy hair (Cc) Curly (CC) X Straight (cc)= Wavy hair (Cc)

19 X-linked X-linked –Genes are linked to x-chromosome –Colorblindness Recessive Recessive Unable to distinguish certain colors, eg. green or red Unable to distinguish certain colors, eg. green or red

20 Sex-influence traits Sex-influence traits –Males and females can show different phenotypes even with same genotypes –Autosomal –Type of Baldness Dominant in males Dominant in males Recessive in females Recessive in females

21 Chromosomal disorders Chromosome problems, not genes Duplication – a repeat of several gene sequences on the same chromosome Deletion – loss of a chromosome segment

22 Inversion – gene sequence separated from chromosome, reinserted into same place, but in reverse Translocation – transfer of one chromosome part to a non-homologous chromosome

23 Chromosome number disorders Nondisjunction – one or more pairs of chromosomes fail to separate during mitosis or meiosis (produces condition known as aneuploidy – more or less chromosomes than the parental number) Down Syndrome – one extra chromosome at #21

24 Sex Chromosome number changes Turner syndrome – inheriting only one X chromosome with no additional X or Y chromosome Most X0 zygotes spontaneously abort 0.01–0.04% of females Non-functional ovaries (infertile) Short height Normal intelligence

25 Kleinfelter Syndrome – one extra X chromosome with normal XY (XXY) % of males Conditions develop after puberty Smaller testes - usually sterile (not always) Taller than normal Normal intelligence Very subtle phenotype characteristics

26 XYY Condition – extra Y chromosome as result of non-disjunction 0.1% of males Taller than average Mild retardation

27 Detection Amnioncentesis Amnioncentesis –Removal of amniotic fluid from the amnion, the sac surrounding the fetus –Between 14 – 16 week of pregnancy

28 Chorionic villi sampling Chorionic villi sampling –Cells derived from the zygote that grow between uterus and placenta –Between 8 th and 10 th week

29 Genetic counseling Genetic counseling –Informing a person or couple about their genetic makeup –Form of medical guidance about problems that might affect their offspring

30 Treatment Usually treat symptoms Usually treat symptoms Gene therapy Gene therapy –Replacement of defective genes with a healthy one –Somatic cell gene therapy (body cells) –Germ cell gene therapy (eggs or sperms) Poses risks and ethical issues Poses risks and ethical issues


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