Another gene involved in baldness is the Androgen receptor (AR) gene. It is sex- linked; more specifically, X-linked. A bit of review: what does it mean to be sex- linked? PAX1 has alleles P (wild-type) and p (mutant); AR has alleles a (wild-type) and A (mutant). Each mutant allele increases your risk of baldness by 0.1%. What is the genotype of a male with the highest likelihood of being bald?
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The evidence that male pattern baldness is genetically heterogeneous is that it has an adult onset: hormones exert an environmental effect: causative genes are found on the X and the Y chromosomes. More than one gene has variants that increase the risk of becoming bald. It can be transmitted from one gender to the other. The evidence that male pattern baldness is incompletely penetrant is that inheriting variants of two genes increases risk. Not everyone who has genotypes associated with baldness actually loses their hair. Certain drugs can restore some hair growth. It can be caused by a mutation in a gene on the X chromosome. It can be inherited as a recessive trait in women but a dominant trait in men. The DNA test results come back. Roger does not have the SNPs associated with the region on chromosome 3 that increases the risk of male pattern baldness, but he does have the combination of a mutation in the androgen receptor gene and the telltale SNP pattern from one chromosome 20 that greatly elevates risk. An inheritance pattern consistent with these results is Roger inheriting the androgen receptor gene mutation from Sarah, who likely got it from her bald father; and inheriting the chromosome 20 risk allele from Abe, who likely got it from his mother, Martha, because his father has the lovely red locks. Roger also inherits the androgen receptor gene mutation from his father, Abe, who got it from his father, Emmett; and inherits the susceptibility region of chromosome 20 from his mother, Sarah, who got it from her bald father, George. Roger inherits the susceptibility region of chromosomes 3 and 20 from his mother, Sarah, who inherited one from each of her parents. He inherits the wild type androgen receptor gene variant from his father, Abe, and the mutant variant from his mother, Sarah. He inherits the androgen receptor mutation from his father because he inherits his father's Y chromosome, and the high-risk SNPs from his mother's X chromosome.
Sri K.
Like most traits, baldness is controlled by multiple genes. A GWAS study of male baldness in people of European ancestry showed that the locus with the greatest correlation was on the X-chromosome. Thus, weirdly, men often inherit their baldness from their mom! The SNP that was most correlated with baldness is called rs2497938. There are two alleles: "C", which is the dominant allele and "T", which is the recessive allele and increases the likelihood of baldness. So, men with an XTY genotype have an increased likelihood of baldness. In a survey of a US population of European descent, 69.2% of females were homozygous for the recessive allele. What percentage of males should have an increased chance of baldness assuming the population is at Hardy-Weinberg Equilibrium? Enter the number as a percentage with two decimal places.
Katlin K.
In humans there is a genetic form of premature baldness that is due to an autosomal recessive gene allele (b). This is a sex-limited trait- it only appears in males. Imagine a man with a full head of hair (Bb genotype) mates with a woman who also has a heterozygous (Bb genotype). What phenotypes do you expect in their children?
Jennifer H.
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