1. Chromosomes and Human Genetics 10.4-10.5 12.2-12.3 Prenatal Diagnosis
College Prep Biology
Mr. Martino

2. Introduction
Karyotype: photograph of special organization of metaphase chromosomes
Paired with homologue
Autosomes arranged from largest to smallest
Sex chromos. are last pair
Used to detect genetic disorders

3. 10.4 Chromosomal Basis of Inheritance
Autosomes: the chromsomes (numbered 1 – 22) that are determine all traits but sex - homologous
Sex chromsomes: 23rd pair of chromos. that determine sex in humans
Females: XX (homo. chromos.)
Males: XY (non homo. chromos.)

4. 10.4 Sex Determination in Humans
Different species have different sex determination systems
Humans have XY system – males determine sex as do spinach, grasshoppers, crickets, and roaches
Females determine sex in fishes, birds, strawberries, and butterflies
Most plants (monoecious) and some animals (hermaphrodites) do not have separate sexes.
Ex. Corn, earthworms and snails

5. 10.5 Linked Genes
1908 – William Bateson and Reginald Punnett discovered inheritance that contradicted Mendelian principles
F2 generation should have been 9:3:3:1 – but it was 3:1
Discovered these genes are on the same chromosome
Linked Genes: genes found on the same chromosomes
inherited together

6. Early 1900’s, Thomas Hunt Morgan discovered crossing over
Used Drosophila melanogaster
Offspring should have been 1:1:1:1, but were not
Crossing over: is the exchange of corresponding segments between two homologous chromosomes
Effects several genes at once
Genetic Recombination: the production of gene combos different from those carried by the original chromosomes

7. Pedigrees Males are squares Females are circles
Pedigree: a tool used to assemble a family’s history in a family tree
Males are squares
Females are circles
Full shade represent afflicted
Partial (if present) represent carriers
Marriage lines join parents on sides
Sibling lines join siblings at top

8. 10.5 Inheritance Patterns
Autosomal Recessive: any recessive trait carried on a regular chromosome
Ex. Cystic fibrosis, PKU, albinism
Autosomal Dominant: any dominant trait carried on a regular chromosome
Ex. Polydactyly, Huntington’s, achondroplasia

9. Sex-linked traits
Sex-linked traits: are determined by genes located on the sex chromosomes
Usually the X
Ex. Fruit fly eye color, hemophilia, some colorblindness, red feline coat color

12. Hutchinson-Gilford progeria syndrome
Autosomal dominant- individual only needs one dominant allele to show the trait
Result of mutation
Usually die in early teens
Both boys pictured are not yet 10…both died while in their teens of complications with old age

13. Changes in Chromosome Structure
Occasionally chromo. structure is altered
1. Deletion: loss of a chromosome segment
2. Duplication: gene sequences that are repeated
3. Inversion: section of DNA is reversed
4. Translocation: broken piece of chromo. attaches to nonhomo. chromo.

15. Do Changes in Chromosome Structure Ever Evolve?
Most chromo. changes tend to be selected against
Duplications seem to be the exception
Duplications may provide opportunity for beneficial mutations – still have at least one good gene
Several seem to be pivotal in evolution
Duplications, inversions, & translocations helped
Of our 23 pairs of chromos. 18 are virtually identical to chimps & gorillas – other 5 differ at inverted and translocated regions

16. Changes in Chromosome Number
Aneuploidy: when there is an incorrect number of chromos.
Major cause of reproductive failures
Polyploidy: having 3 or more of each type of chromo.
Possible in plants
Occurs in some insects, fishes, etc.
Lethal in humans – only 1% survive to birth

17. Nondisjunction: one or more pairs of chromosomes fail to separate during meiosis
Down’s syndrome (Trisomy 21)
Turner’s syndrome – females that have only 1 X
Klinefelter’s Syndrome – males have 2 X’s

18. Prospects in Human Genetics
Abortion: removal of a fetus from the uterus
Genetic Screening: carriers are identified in order to learn the probability of certain disorders in offspring
Genetic Counseling: diagnosis, pedigree, genetic testing for parents with potential to pass on severe genetic disorders

19. Ultrasound: uses sound waves to produce image of fetus
Prenatal Diagnosis: there are several methods available to determine many different genetic disorders before birth
Ultrasound: uses sound waves to produce image of fetus
No known risks
takes measurements
Routine in pregnancies and may detect fetal problems
Amniocentesis: withdrawal of some amniotic fluid containing fetal cells for karyotype
must be weeks
Results take several weeks
1% risk of miscarriage

20. Chorionic Villi Sampling (CVS): a tube is inserted into cervix & a small amount of chorion is removed
This is fetal tissue and DNA
8 – 10 weeks
Results in hours
2% miscarriage risk
Fetoscopy: a needle-thin tube is inserted into uterus for direct veiwing
10% miscarriage risk
In-vitro fertilization: fertilize egg in lab and select zygotes with no disorder to implant into mother

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