Chromosomes, Genes, Alleles and Characteristics Flashcards
What is DNA
Deoxyribonucleic acid (=DNA) is the molecule
in the nucleus that carries our genetic code.
Fertilisation
Woman–> egg(ovum)
23 chromosomes-]
]
]—FERTILISATION
]. Zygote{46 chromosomes in 23 pairs}—->embryo
]. {46 chromosomes in 23 pairs}
]
Man—–> sperm. ]
23 chromosomes-]
How many chromosomes does a female egg [ovum] have?
23 chromosomes
How many chromosomes does a male sperm cell have?
23 chromosomes
How many chromosomes does a zygote have?
46 {but in 23 pairs}
How many chromosomes does an Embryo have?
46 {but in 23 pairs}
What is a Chromosome?
A chromosome is a length of DNA.
• Chromosomes are arranged into pairs in
the nucleus.
• Along the length of each chromosome are
coding regions called genes.
• Each gene codes for a specific protein –
which give us our unique characteristics.
What is a gene?
Genes are small sections of
chromosomes (DNA) that code for a
particular characteristic. (protein)
• Genes contain a code that code for a
particular sequence (chain) of amino
acids.
• This sequence of amino acids makes
a specific protein.
What is an allele?
• An allele is a different/alternate form of a gene.
• E.g. if the gene is eye colour the alleles could be:
• Brown allele
• Blue allele
• Green allele
What is an allele? {part 2}
• Homozygous alleles are two alleles that are the same. E.g. BB, TT, cc
• Heterozygous alleles are two alleles that are different. E.g. Bb, Tt,
Cc.
Dominant and Recessive alleles
• Dominant alleles are always expressed if they are
present.
• Recessive alleles are only expressed if there are 2
recessive alleles present.
• If an individual has 2 alleles the same (e.g. BB, tt etc)
this is called homozygous alleles.
• If an individual has 2 different alleles (e.g. Bb, Tt etc)
this is called heterozygous alleles.
