Inheritance, variation and evolution (B2.6) Flashcards
What is a gene?
A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.
What is an allele?
Different versions of a gene we have 2 alleles per gene( 1 from each parent)
What is a genotype?
The alleles for a specific characteristic that are present
What is a gamete?
Gametes are sex cells eg sperm and egg cells but are not fused together.
They have 23 chromosomes (one copy of each chromosome called a chromatid)
What is a diploid and a haploid?
A gamete is a haploid as haploids are a single set of chromosomes of 23.
When the two gametes combine, they merge the two sets of chromosome to have 46, which are referred to as diploid. This produces a new cell called a zygote
What is a phenotype?
Observable physical characteristics as a result of genes
What is meant by a dominant allele?
The dominant allele is always expressed and is (B) even if only one copy is present
What is meant by a recessive allele?
The recessive allele needs 2 recessive alleles to be expressed (b)
What is meant by homozygous?
2 of the same alleles( bb= homozygous recessive or BB= homozygous dominant)
What is meant by heterozygous dominant?
Different alleles (Bb)
How many chromosomes do human cells have in their nucleus?
23 pairs (46)
What is sexual reproduction?
What is 2 advantages and 2 disadvantages?
2 parents have sex by mixing 2 sets of genetic information from 2 gametes and the offspring is genetically different
ADV- variation in offspring DIS- slower to reproduce and we need 2 partners.
What is asexual reproduction?
What is 2 advantages and 2 disadvantages?
1 parent makes identical copies of its cells and DNA and the offspring is identical to the parent (no gametes are required)
ADV- quick and no partners DIS- no variation and offspring will inherit diseases
What are the male and female sex organs in plants?
Male= stamen and female= stigma
Describe how sexual reproduction occurs and what type of cell division is used:
The gametes from each parent fuses and forms a zygote. Meiosis occurs
Describe the process of Meiosis
Cells in reproductive organs divide by meiosis to form gametes. Two cell divisions occur and the chromosomes replicate but only 1/2 of each chromosome goes to a new daughter cell. 4 new daughter cells are produced and the daughter cells are genetically different.
Describe the rough process of Mitosis
Only 1 cell division occurs and it produces 2 genetically identical daughter cells. The cell which has 46 will double to 92 and the split into 2 cells each of 46.
The chromosomes replicate which copies all genetic information (as a chromatid) and goes to each new daughter cell.
Why does Mitosis occur?
During growth, repair and asexual reproduction
Why does meiosis occur?
Meiosis only occurs in reproductive cells so the ovaries and testes in humans, to create haploid gametes that will be used in fertilisation
What is a chromatid?
one copy of each chromosome
Describe the organisation of our structure from small to large (8)
Genes, DNA, Chromosomes, Nucleus, Cell, Tissue, Organ , Organism
What is DNA?
Deoxyribonucleic acid. The genetic material in the nucleus of a cell is composed of DNA. DNA is made up of two strands forming a double helix. The DNA is contained in structures called
chromosomes.
What are the sex organs in flowering plants?
pollen and egg cells
What happens after meiosis?
Gametes join at fertilisation to restore the normal number of chromosomes. The new cell divides by mitosis. The number of cells increases and are identical. As the embryo develops cells start to differentiate.