lecture 4 Flashcards
1
Q
chromosome theory of inheritance
A
- mendelian genes have specific loci on chromosomes
- chromosomes undergo segregation and independent assortment
- behaviour said to account for mendel’s laws of segregation and independent assortment
2
Q
mendell’s laws
A
- segregation
– two alleles for each gene separate during gamete formation - independent assortment
– alleles of genes on nonhomologous chromosomes assort independently during gamete formation
3
Q
morgan’s experiment
A
- first solid sceintific evidence associating gene with specific chromosome
- fruit fly experiment
- breed high rate
- 4 pairs of chromosomes (3 autosomes, 1 sex chromosomes)
- normal or wild phenotype, mutant phenotypes
– F1 all red eyes
– F2 3:1 red:white, only males with white
– white-eyed gene on X chromosome - P = R x W
– f1 = 4 R
– f2 = 3 R ; 1 W
4
Q
humans
A
- two varieties of sex chromosomes (larger X, smaller Y)
- only ends of Y have regions that are homologous with X
- SRY gene, Y codes for development of testes
- female = XX
- male = XY
- ovum have X, sper have X or Y
5
Q
systems of sex determination
A
- humans
– X-Y system: 22X (or) 22Y sperm; 22X egg
– 44 XX (or) 44XY zygote - crickets
– X-0 system: 22XX female; 22X male - birds, some fish, insects, reptiles and crustacea
– 76 ZW female, 76 ZZ male
– males homogametic - bees
– haploid-diploid system: 32 (2N) female; 16 (N) male
6
Q
disorders by recessive alleles on X chromosome
A
- colour blindness
- duchenne muscular dystrophy
- hemophilia
7
Q
inactivation in female mammals
A
- one of two X chromosomes in each cell randomly inactivated during embryonic development
- inactive X condenses into Barr body
- if femal is heterozygous for particular gene on X chromosome, will be a mosaic for that character
8
Q
linkage affects inheritance
A
- morgans experiment
– crossed flies with different body colour and wing size - wild type (gray, normal wings) x dbl mutant (black, vestigial wings)
- f1: dihybrid (wild type) x dbl mutant
- f2: wild type, black vestigial, gray vistigial, black normal
- do not assort independently
- genetic recombination: combination of traits differing from either parent
9
Q
recombination of unlinked genes
A
- offspring with phenotype matching parental phenotype called parental types
- offspring with nonparental phenotypes called recombinant types/recombinants
- 50% of recombination
10
Q
- fruit example
A
- genes can be linked, by linkage incomplete as evident for recombinant phenotypes
- crossing over of homologous chromosomes (breaks physical connection between genes)
11
Q
crossing over example
A
- farther apart two genes are, higher probability that crossover will occur (higher recombination frequency)
12
Q
genetic maps example
A
-
13
Q
alterations of chromosome number
A
- large-scale alterations lead to spontaneous abortions/ variety of development disorders
- nondisjunction: pairs don’t separate normally during meiosis (gamete receives two of same type chromosome, other no copy)
- aneuploidy: fertilisation of gametes in which nondisconjunction occured (abnormal number of particular chromosomes)
– monosomic: one copy of particular chromosome
– trisomic: three copies of particular chromosome - polyploidy: more than two complete sets of chromosomes
– 3N; 4N
– common in plants (not animals)
14
Q
alterations of chromosome structure
A
- breakage of chromosome:
– deletion (removes segment)
– duplication (repeats segment)
– inversion (reverses a segment in chromosome)
– translocation (moves segment from one chromosome to another)
15
Q
human disorder from chromosomal alterations
A
- down syndrome
– aneuploid condition: three copies of chromosome 21 - klinefelter syndrome
– extra chromosome in male (XXY)
– sterile, some female traits - monosome X (turner syndrome)
– X0 females; sterile - cri du chat
– deletion of chromosome 5
– mentally retarded, catlike cry, die early childhood/infancy - CML
– translocation of chromosomes
