B1h - Variation And Inheritance Flashcards
How many chromosomes (in pairs) do humans have?
46
How many chromosomes are in gametes?
23
What is variation caused by?
- genes being mixed up when gametes are formed
- genes coming from two parents (fertilisation)
- changes in genes or chromosomes (mutations)
What is the debate over the relative importance of genetic and environmental factors in some humans?
Debate over genetic (nature) and environmental (nurture) factors in determining human attributes e.g. Intelligence, sporting ability, health
What are alleles?
Different versions of the same gene
How is sex in mammals determined by sex chromosomes?
XX (female)
XY (male)
How do dominant and recessive characteristics depend on dominant and recessive alleles?
- dominant alleles are those expressed if present
- recessive alleles are those only expressed if the dominant allele is absent
What is a monohybrid cross?
Involves different alleles of a gene. Carried out on a pair of chromosomes: one could be carrying the dominant allele and the other can be carrying the recessive allele
What is homozygous?
Two identical alleles
What is heterozygous?
Two different alleles
What is genotype?
The genetic makeup
What is phenotype?
The characteristics expressed
How are there different sexes?
Each egg carries one type of sex chromosome (X). Each sperm carries either a X or a Y sex chromosome
What is dominant?
Stronger characteristic
What is recessive?
Weaker characteristic
