Genetics: Mendelian Inheritance, Dominant vs Recessive Genes, Autosomal vs Allosome Chromosomes

In this video I go over genetics, which is the study of inheritance, and specifically look at Mendelian inheritance in which genes and traits are passed on from parents to offspring. Genes are regions of DNA that specify traits of an organism. Genes have variants, called alleles, and each chromosome can only carry one allele for each gene. Alleles are passed from parents to offspring depending on if one is dominant or recessive. I describe how alleles are passed on to the offspring for both autosomal (non-sex) and allosomal (sex) chromosomes. Finally, I show how Punnett squares can be used to predict the phenotypes (physical traits) of test crosses of organisms.

Time stamps:

• Genetics is the study of inheritance. Mendelian inheritance is the process by which genes and traits are passed from parents to offspring: 0:00
• Allele is 1 or more forms of a gene variant: 1:32
• Dominance is the phenomenon of one allele on a chromosome masking or overriding the effect of a different allele of the same gene on the other copy of the chromosome. The second allele is recessive: 2:40
• Autosomal (non-sex chromosome) dominant and recessive inheritance diagram: 3:27
• Penetrance is proportion of individuals carrying an allele that also express the associated trait (phenotype): 7:04
• Expressivity is the degree to which a phenotype is expressed by individuals with a particular genotype: 8:45
• Law of segregation states that alleles for each gene segregate from each other so that each gamete carries only one allele for each gene: 9:32
• Law of independent assortment states that genes of different traits can segregate independently during the formation of gametes (except for sex-linked traits): 11:30
• Sex linked describes the sex-specific patterns of inheritance when an allele is present on an allosome (sex chromosome, which determine the sex of the organism): 12:16
• Human genome has 22 pairs of autosomes and 1 allosome pair (47 chromosomes total): 14:33
  • Females have XX allosomes pair. Males have XY allosomes pair: 15:04
  • X chromosome has more than 153 million base pairs. Y chromosome has 59 million base pairs: 16:06
  • Sex chromosomes of fruit flies diagram: 18:36
• Karyotype ordering of chromosome pairs diagram for humans: 22:36
• Karyogram ordering from a micrograph for a human male: 23:46
• X-linked recessive inheritance phenotype is always expressed in mailed because they only have one X chromosome: 26:05
• X-linked dominant inheritance has the dominant gene carried on the X chromosome: 31:23
• Y-linked inheritance describes traits produced by genes on the male Y-chromosome: 33:52
• Punnett square can be used to predict the results of a test cross: 35:45
  • In a test cross, the individual is bred with another individual that is homozygous for the recessive trait: 37:47

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