Bio 15 - Genetics Flashcards
What is a chromosome ?
A complex of DNA and proteins (including histone proteins)
What is a gene ?
A sequence of DNA that codes for a protein or polypeptide
What is a locus ?
The position of a gene on a DNA molecule
What is meant by a homologous pair of Chromosomes ?
Humans inherit 46 chromosomes - 23 maternal and 23 paternal.
A given chromosome from maternal origin has a counter-part from paternal origin which codes for the same product.
What is an Allele ?
Any homologous pair of chromosomes having a pair of genes (allele) which codes for the same product (ie. hair colour)
Describe Homozygosity ?
When both alleles coding for a gene are identical
Describe Heterozygosity
When the alleles coding for a gene are different
What is the genotype ?
The set of genes possessed by a particular organism.
What is the phenotype ?
The expression of the genotype (may also have environmental influences!)
Explain dominant and recessive alleles ?
In a heterozygous genotype, the expressed gene is the dominant allele while the other is the recessive.
This is also known as Mendel’s law of dominance.
What is the convention for symbolising dominant and recessive genes ?
A - dominant
a - recessive
Explain incomplete or co-dominance ?
Each individual carries two alleles, while populations may have many or multiple alleles.
Sometimes these genes aren’t strictly dominant or recessive.
There may be degrees of blending (incomplete dominance) or two alleles may be equally dominant (co-dominant). E.g. ABO blood types
What happens to the phenotype when two dominant alleles are present ?
The contributions of both alleles do not overpower each other, the phenotype is a result of the expression of both alleles.
Describe the genotype, antigens and antibodies present in the Phenotype Blood group A ?
Describe the genotype, antigens and antibodies present in the Phenotype Blood group B ?
Describe the genotype, antigens and antibodies present in the Phenotype Blood group AB ?
Describe the genotype, antigens and antibodies present in the Phenotype Blood group O ?
What is the universal donor ?
O negative - no antigens !
What is the universal recipient ?
No antibodies
Describe Rhesus factors ?
Coded for by different genes at different loci to A and B antigens
What %age of the population are Rh+ ?
85%
What is erythroblastosis fatalis ?
If and Rh- woman has been exposed to Rh+ blood, she will then have antibodies in her blood.
If her fetus is Rh+ antibodies may cross the placenta and cause the fetus erythrocytes to agglutinate.
What is Mendels first law of segregation ?
In gametogenesis, homologous chromosomes separate during the first meiotic division, therefore alleles coding for the same trait are segregated.
What is Mendel’s second law of independent assortment ?
Different chromosomes separate independently of each other, e.g. paternal and maternal chromosomes don’t all end up in seperate spermatocytes
Each chromosome in a homologous pair separates independently of any other chromosome in other homologous pairs
What is “crossing over” ?
When homolgous chromosomes exchange parts
What is linkage in terms of genetics ?
The propensity for some genetic traits to refrain from assorting independently
What is a “double crossover” ?
When two crossovers happen in a chromosomal area being studied.
Why is sex linkage an exception to Mendel’s law ?
Some traits follow the inheritance of the sex chromosomes.
Describe human sex chromosomes ?
1 pair
XX = Female XY = Male