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Inheritance Principles and Human Genetics

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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 Studied fruit flies
Found X and Y chromosomes After the “rediscovery” of Mendel’s pea plants research – Morgan studied fruit flies in the early 1900’s

4 Karyotypes Karyotyping is a process that allows chromosomes to be presented in an orderly, easily compared manner This karyotype is of a female (XX)

5 Sex chromosomes (X, Y) Autosomes
Contain genes that determine the sex (gender) of an individual Autosomes Not directly involved in determining the sex of an individual Different organisms, different number X Y The X chromosome contains over 800 genes. The Y chromosome contains less than 50 genes (as of 2010).

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

7 Gene location 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) Studying sex-linked traits allowed a better understanding of where genes are located on chromosomes

8 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 Map unit – frequency of crossing over of 1%.

10 Mutations Germ-cell mutations Somatic-cell mutations
Occur in gametes (may not be expressed until offspring) Somatic-cell mutations Occur in body cells May affect organs Skin cancer and leukemia Lethal mutations Cause death, often before birth Either mutation may affect “control genes” that cause changes to many other genes

11 Inheritance of Traits 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 Autosomal Appears in both sexes equally Dominant Every individual with the trait will have parents with the trait BB or Bb (dominant trait will show) bb (recessive trait will show) 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 Controlled by a single allele of a gene More 200 human traits Huntington’s disease Forgetfulness and irritability

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

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

17 Multiple Alleles Codominance Genes with 3 or more alleles
ABO blood groups IA, IB, and I IA and IB are codominant Codominance Both alleles are expressed IAIB is type AB

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

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

20 Sex-influence traits Males and females can show different phenotypes even with same genotypes Autosomal Type of Baldness Dominant in males 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
Removal of amniotic fluid from the amnion, the sac surrounding the fetus Between 14 – 16 week of pregnancy

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

29 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 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

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