Heredity (Inheritance) (Questions) Flashcards
What is inheritance/heredity?
Inheritance is the transfer of genetically determined characteristics encoded by genes from one generation to the next.
What is genetics?
Genetics is the study of inheritance.
How many chromosome pairs are present in humans, and how are they classified?
Humans have 23 chromosome pairs: 22 homologous pairs (autosomal) and 1 pair of sex chromosomes (XY or XX).
What are alleles?
Alleles are different versions of a gene occupying the same locus on homologous chromosomes.
What is the difference between homozygous and heterozygous alleles?
Homozygous alleles are the same version of a gene on both homologous chromosomes (e.g., BB or bb), while heterozygous alleles are different versions of the same gene (e.g., Bb).
What is a genotype?
A genotype is the genetic makeup of an organism, indicating which alleles are homozygous and which are heterozygous (e.g., BB, Bb, bb).
What is a phenotype?
A phenotype is the observable expression of a genotype, reflecting characteristics like hair color (e.g., black hair).
What is a dominant allele, and how is it expressed?
A dominant allele (e.g., B) is expressed in the phenotype regardless of the other allele present. It is expressed in BB or Bb genotypes.
What is a recessive allele, and when is it expressed?
A recessive allele (e.g., b) is expressed in the phenotype only if it is present on both alleles (bb).
What is a Punnett square used for?
A Punnett square is used to determine the probability of inheritance and to predict the offspring’s genotype and phenotype.
What is the genotype and phenotype outcome of a cross between BB and bb?
Offspring genotype = 100% Bb (heterozygous); offspring phenotype = 100% black hair.
What are the offspring’s genotype and phenotype when crossing two Bb parents?
Offspring genotype: 25% BB (homozygous dominant), 50% Bb (heterozygous), 25% bb (homozygous recessive); phenotype: 75% black hair, 25% blonde hair.
What is X-linked inheritance?
X-linked inheritance refers to the inheritance of traits determined solely by genes on the X chromosome, such as hemophilia and color blindness.
How do XY and XX chromosomes differ in terms of gene expression?
In XY chromosomes, if a gene is X-linked, its expression is not masked because there is no corresponding allele on the Y chromosome. In XX chromosomes, alleles are homologous.
What are the possible genotypes and phenotypes for color blindness (X-linked trait)?
- XN XN: not color blind (homozygous dominant)
- XN Xn: not color blind (heterozygous carrier)
- Xn Xn: color blind (homozygous recessive)
- XN Y: not color blind (one copy of the dominant allele)
- Xn Y: color blind (one copy of the recessive allele, no gene on Y to mask the recessive gene on X)
