Chapter 3.4 Inheritance Flashcards Preview

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Flashcards in Chapter 3.4 Inheritance Deck (15):


discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed



the symbolic representation of the pair of alleles possessed by an organism, typically represented by two letters ex: Bb, GG, tt



the characteristics or traits of an organism. ex: 5 fingers on each hand, colour blindness, type O blood.


Dominant allele

An allele that has the same effect on the phenotype whether it is paired with the same allele or a different one. Dominant alleles are always expressed in the phenotype
ex: the genotype Aa gives the dominant A trait because the a allele is masked, the a allele is not transcribed or translated during protein synthesis


Recessive allele

an allele that has an effect on the phenotype only when present in the homozygous state. ex: aa gives rise to the recessive trait because no dominant allele is there to mask it.


Co-dominant alleles

pairs of alleles that both affect the phenotype when present in a heterozygote. ex: a parent with curly hair and a parent with strait can have children with different degrees of hair curliness, because both alleles influence hair condition when both are present in the genotype.



the particular position on homologous chromosomes of a gene. Each gene is found at a specific place on a specific pair of chromosomes



having two identical alleles of a gene. ex: AA is a genotype that is homozygous dominant, whereas aa is the genotype of someone who is homozygous recessive for that trait.



Having two different alleles of a gene. This results from the fact that the paternal allele is different from the maternal one. ex: Aa is a heterozygous genotype



An individual who has a recessive allele of a gene that does not have an effect on the phenotype. ex: Aa carries the gene for albinism but has pigmented skin, which means an ancestor must have been albino and some offspring might be albino; if both parents are unaffected by a recessive condition yet both are carriers, some of their offspring could be affected.


Test cross

Testing a suspected heterozygote plant or animal by crossing it with known homozygous recessive (aa). Because a recessive allele can be masked, it is often impossible to tell whether an organism is AA or Aa unless they produce offspring that have the recessive trait. An example of a test cross is shown later in this section when we explore three generations of pea plants.


Punnett grid

to show all the possible combinations of genetic information for a particular trait in a monohybrid cross. A monohybrid cross is one in which the parents have different alleles and which shows the results for only one trait.


Autosomal Recessive Diseases

Diseases caused by recessive alleles and the locus of their gene is found on one of the first 22 pairs of chromosomes but not on the sex chromosomes X and Y. (albinism, cystic fibrosis, sickle cell disease, phenylketonuria, Tay Sachs disease, Thalassemia)


Sex Linked genetic trait

genetic trait whose gene has its locus on the X or the Y chromosome. Often genetic traits that show sex linkage affect one sex more than the other: Color Blindness and Hemophilia.



a disorder in which blood does not clot properly.